I'm just reading the Harry Potter books and what is Professor McGonagall's position? I know Dumbledore is the head, but is she slightly higher than Snape or any of the others?
Yes, Professor McGonagall is higher than most in the org chart
As Oak points out in comments, McGonagall is Gryffindor's Head of House:
Professor McGonagall was head of Gryffindor House, but it hadn't stopped her from giving them a huge pile of homework the day before.
Harry Potter and the Philosopher's Stone Chapter 8: "The Potions Master"
It's unclear whether or not Head of House is a higher position than a regular professor, but it does include additional duties (a certain degree of management of the Prefects and the common room, and serving as a sort of guidance counsellor for students). To the extent it is considered a higher position, this alone sets her higher than most other professors; all except for the Heads of the other three houses.
As well, Professor McGonagall is the Deputy Headmistress (bold is my emphasis, italic is from the text):
Dear Mr. Potter,
We are pleased to inform you that you have been accepted at Hogwarts School of Witchcraft and Wizardry. Please find enclosed a list of all necessary books and equipment.
Term begins on September 1. We await your owl by no later than July 31.
Harry Potter and the Philosopher's Stone Chapter 4: "The Keeper of the Keys"
Which sets her higher than all of the other professors. One of her additional duties is to fill in for an incapacitated Head Teacher, until a permanent replacement can be appointed; she does this in Chamber of Secrets, when Lucius Malfoy has had Dumbledore removed:
"I always thought Father might be the one who got rid of Dumbledore," [Malfoy] said, not troubling to keep his voice down. "I told you he thinks Dumbledore's the worst headmaster the school's ever had. Maybe we'll get a decent headmaster now. Someone who won’t want the Chamber of Secrets closed. McGonagall won’t last long, she's only filling in..."
Harry Potter and the Chamber of Secrets Chapter 15: "Aragog"