Ancient Runes is purely a language course. We can see this from the numerous if disperse references to it throughout canon.
Book 3 - Harry Potter and the Prisoner of Azkaban said:
“Every night, without fail, Hermione was to be seen in a corner of the
common room, several tables spread with books, Arithmancy charts, rune
dictionaries, diagrams of Muggles lifting heavy objects, and file upon
file of extensive notes; she barely spoke to anybody and snapped when
she was interrupted.
Book 3 - Harry Potter and the Prisoner of Azkaban said:
“Harry looked around at the cluttered table, at the long Arithmancy
essay on which the ink was still glistening, at the even longer Muggle
Studies essay (‘Explain Why Muggles Need Electricity’) and at the rune
translation Hermione was now poring over.
Book 3 - Harry Potter and the Prisoner of Azkaban said:
“Why don’t you just drop a couple of subjects?” Harry asked, watching
her lifting books as she searched for her rune dictionary.
Book 3 - Harry Potter and the Prisoner of Azkaban said:
Ron threw something down onto Hermione’s rune translation. Hermione
and Harry leaned forward. Lying on top of the weird, spiky shapes were
several long, ginger cat hairs.
Book 4 - Harry Potter and the Goblet of Fire said:
“Well, now we know what to do next time I can’t manage a spell,” Harry
said, throwing a rune dictionary back to Hermione, so he could try
again, “threaten me with a dragon. Right…” He raised his wand once
more. “Accio Dictionary!” The heavy book soared out of Hermione’s
hand, flew across the room, and Harry caught it.
Book 5 - Harry Potter and the Order of the Phoenix said:
Harry did not read any further. Fudge might have many faults but Harry
found it extremely hard to imagine him ordering goblins to be cooked
in pies. He flicked through the rest of the magazine. Pausing every
few pages, he read: an accusation that the Tutshill Tornados were
winning the Quidditch League by a combination of blackmail, illegal
broom-tampering and torture; an interview with a wizard who claimed to
have flown to the moon on a Cleansweep Six and brought back a bag of
moon frogs to prove it; and an article on ancient runes which at least
explained why Luna had been reading The Quibbler upside-down.
According to the magazine, if you turned the runes on their heads they
revealed a spell to make your enemy’s ears turn into kumquats. In
fact, compared to the rest of the articles in The Quibbler, the
suggestion that Sirius might really be the lead singer of The
Hobgoblins was quite sensible.
This is just another example of reading runes. Admittedly, in this case, upside down and in the Quibbler. The article is called ‘Secrets of the Ancient Runes Revealed’.
Book 5 - Harry Potter and the Order of the Phoenix said:
Every single Divination and Care of Magical Creatures lesson was now
conducted in the presence of Umbridge and her clipboard. She lurked by
the fire in the heavily perfumed tower room, interrupting Professor
Trelawney’s increasingly hysterical talks with difficult questions
about ornithomancy and heptomology, insisting that she predicted
students’ answers before they gave them and demanding that she
demonstrate her skill at the crystal ball, the tea leaves and the rune
stones in turn.
Divination can apparently involve ‘rune stone’. What a rune stone is, or if they are any relation to study of ancient runes, is unclear. Whatever the case, runes as an ancient form of writing still works fine in this instance. No one is claiming tea leaves can be used to cast powerful magic; it’s just a way of making random shapes, or in the case of runes, letters.
Book 5 - Harry Potter and the Order of the Phoenix said:
“She’s been breaking into your broom shed in the garden since the age
of six and taking each of your brooms out in turn when you weren’t
looking,” said Hermione from behind her tottering pile of Ancient Rune
books.
“Oh,” said George, looking mildly impressed. “Well - that’d explain
it.”
“Has Ron saved a goal yet?” asked Hermione, peering over the top of
Magical Hieroglyphs and Logograms.
According to Wikipedia, “A logogram, or logograph, is a grapheme which represents a word or a morpheme (the smallest meaningful unit of language).” Likewise, a hieroglyph is just a method of writing. So this Ancient Runes book (as identified in the first paragraph) is about the Hieroglyphs and Logograms used in the magical world.
Book 5 - Harry Potter and the Order of the Phoenix said:
“That’s the trouble with Quidditch,” said Hermione absent-mindedly,
once again bent over her Runes translation, “it creates all this bad
feeling and tension between the houses.”
She looked up to find her copy of Spellman’s Syllabary, and caught
Fred, George and Harry all staring at her with expressions of mingled
disgust and incredulity on their faces.
“Well, it does!” she said impatiently. “It’s only a game, isn’t it?”
“Hermione,” said Harry, shaking his head, “you’re good on feelings and
stuff, but you just don’t understand about Quidditch.”
“Maybe not,” she said darkly, returning to her translation, “but at
least my happiness doesn’t depend on Ron’s goalkeeping ability.”
Notice the repeated references to translation. Also, the book she is using is a Syllabary which Wikipedia defines as “A syllabary is a set of written symbols that represent (or approximate) syllables, which make up words. A symbol in a syllabary typically represents an optional consonant sound followed by a vowel sound.” Again, words not magic.
Book 5 - Harry Potter and the Order of the Phoenix said:
“How were the Runes?” said Ron, yawning and stretching.
“I mistranslated ehwaz,” said Hermione furiously. “It means
partnership, not Defense; I mixed it up with eihwaz.”
The exam includes translation. Nothing else is mentioned.
Book 6 - Harry Potter and the Half-Blood Prince said:
“I know I messed up Ancient Runes,” muttered Hermione feverishly, “I
definitely made at least one serious mistranslation. And the Defense
Against the Dark Arts practical was no good at all. I thought
Transfiguration went all right at the time, but looking back —”
Again, the exam is referenced as containing translation.
Book 6 - Harry Potter and the Half-Blood Prince said:
“Yes, I’ve already agreed it was fishy, Harry,” said Hermione a little
impatiently. She was sitting on the windowsill in Fred and George’s
room with her feet up on one of the cardboard boxes and had only
grudgingly looked up from her new copy of Advanced Rune Translation.
“But haven’t we agreed there could be a lot of explanations?”
Book 6 - Harry Potter and the Half-Blood Prince said:
“We got so much homework for Runes,” she said anxiously when Harry and
Ron joined her. “A fifteen-inch essay, two translations, and I’ve got
to read these by Wednesday!”
Again, Runes is shown, even at NEWT level, to be translations. There is no, ‘practise casting Rune X’.
Book 7 - Harry Potter and the Deathly Hallows said:
“Oh, of course,” said Ron, clapping a hand to his forehead. “I forgot
we’ll be hunting down Voldemort in a mobile library.”
“Ha ha,” said Hermione, looking down at Spellman’s Syllabary. “I
wonder . . . will we need to translate runes? It’s possible. . . . I
think we’d better take it, to be safe.”
She dropped the syllabary onto the larger of the two piles and picked
up Hogwarts, A History.
Spellman’s Syllabary is previously noted as an Ancient Runes textbook. Notice that its sole mentioned use is in translating runes. Also, if runes were used to cast some kind of defensive ‘ward’ magic, as is common in fanon, don’t you think it would be on the ‘definitely take’ list and not the ‘to be safe’ list?
Book 7 - Harry Potter and the Deathly Hallows said:
Scrimgeour now pulled out of the bag a small book that looked as
ancient as the copy of Secrets of the Darkest Art upstairs. Its
binding was stained and peeling in places. Hermione took it from
Scrimgeour without a word. She held the book in her lap and gazed at
it. Harry saw that the title was in runes; he had never learned to
read them. As he looked, a tear splashed onto the embossed symbols.
Runes are for reading, not magicing.
Book 7 - Harry Potter and the Deathly Hallows said:
"And as for this book." Said Hermione, "The Tales of Beedle the Bard …
I've never even heard of them!"
"You've never heard of The Tales of Beedle the Bard?" said Ron
incredulously. "You're kidding, right?"
"No, I'm not," said Hermione in surprise. "Do you know them then?"
"Well, of course I do!"
Harry looked up, diverted. The circumstance of Ron having read a book
that Hermione had not was unprecedented. Ron, however, looked bemused
by their surprise.
"Oh come on! All the old kids' stories are supposed to be Beedle's
aren't they? 'The Fountain of Fair Fortune' … 'The Wizard and the
Hopping Pot'… 'Babbitty Rabbitty and her Cackling Stump'…"
"Excuse me?" said Hermione giggling. "What was the last one?"
"Come off it!" said Ron, looking in disbelief from Harry to Hermione.
"You must've heard of Babbitty Rabbitty –"
"Ron, you know full well Harry and I were brought up by Muggles!" said
Hermione. "We didn't hear stories like that when we were little, we
heard 'Snow White and the Seven Dwarves' and 'Cinderella' –"
"What's that, an illness?" asked Ron.
"So these are children's stories?" asked Hermione, bending against
over the runes. "Yeah." Said Ron uncertainly. "I mean, just what you
hear, you know, that all these old stories came from Beedle. I dunno
what they're like in the original
The Tales of Beedle the Bard is written in runes and it is a book of children’s stories. Likewise, Hermione reads the title as The Tales of Beedle the Bard which is also in runes, as said by Harry.
Book 7 - Harry Potter and the Deathly Hallows said:
Apparently she had not been listening to him. She leaned forward and
held out The Tales of Beedle the Bard.
“Look at that symbol,” she said, pointing to the top of a page. Above
what Harry assumed was the title of the story (being unable to read
runes, he could not be sure), there was a picture of what looked like
a triangular eye, its pupil crossed with a vertical line.
“I never took Ancient Runes, Hermione.”
“I know that; but it isn’t a rune and it’s not in the syllabary,
either. All along I thought it was a picture of an eye, but I don’t
think it is! It’s been inked in, look, somebody’s drawn it there, it
isn’t really part of the book. Think, have you ever seen it before?”
To sum up a very long post: every single instance of runes being used for anything in the books has been about translating them or reading them. So the practical part of the subject is likely just more translation. The only slight exception to this are the runes on Dumbledore’s Pensieve and since they never do anything (glow, pulse etc), and Harry does not read runes (as he states in the above quote), they might say ‘property of Dumbledore’ for all we know.