I know the following
Based on the Portkey writing on Pottermore:
- Almost any object can be made into a Portkey.
Portkeys can be used to travel almost any distance.
Almost any inanimate object can be turned into a Portkey. Once bewitched, the object will transport anyone who grasps it to a pre-arranged destination. A Portkey may also be enchanted to transport the grasper (or graspers) only at a given time.
A Portkey is made with the spell Portus
He [Dumbledore] walked away from the pool to the place where the golden wizard's head lay on the floor. He pointed his wand at it and the muttered, ‘Portus.’ The head glowed blue and trembled noisily against the wooden floor for a few seconds, then became still once more. OotP, Chapter 36
Dumbledore was now rummaging in a cupboard behind Harry and Ron. He emerged from it carrying a blackened old kettle, which he placed carefully upon his desk. He raised his wand and murmured “Portus”; for a moment the kettle trembled, glowing with an odd blue light, then it quivered to a rest, as solidly black as ever. OotP, Chapter 22
The making of Portkey is regulated by the Ministry.
- The Ministry cannot detect the making of an unauthorized Portkey.
‘Now see here, Dumbledore!’ said Fudge, as Dumbledore picked up the head and walked back to Harry carrying it. ‘You haven't got authorization for that Portkey! You can't do things like that right in front of the Minister for Magic, you – you - Ootp, Chapter 36
The question is how much of the destination does the maker of the Portkey need to know about? I.E. Could a wizard who has never been out of Godric's Hollow create a Portkey to New York?
Also, I remember something about the "other half" of the Portkey at destination... can't find any quotes or evidence, so I may just be making things up. This would obviously mean that the maker would have to visit the destination. But this quote from QTtA suggets otherwise
"While there have been no proven referee slayings since , there have been several incidences of broom-tampering over the centuries, the most dangerous being the transformation of the referee's broom into a Portkey, so that he or she is whisked away from the match halfway through and turns up months later in the Sahara Desert."
Related: How and when was the statue head Portkey to Hogwarts set up?
Related: Why is the usage of a Portkey controlled while apparition is free?