In the book, we're told that six professors and the headmaster were tasked with setting up enchantments within Hogwarts to protect the Sorcerer's Stone.
In the film, we only see evidence of five of those.
Harry, Ron, and Hermione encounter Hagrid's three-headed dog named Fluffy, get stuck in Professor Sprout's Devil's Snare, chase after Professor Flitwick's enchanted keys, and play Professor McGonagall's game of Wizard's Chess. Finally, Harry obtains the stone with the help of the Mirror of Erised, Dumbledore's enchantment.
What's missing, though, is a battle with Professor Quirrell's second troll (the trio defeats the first one earlier in the movie), and Professor Snape's potion riddle challenge.
The number of challenges was intentional because seven is considered a magical number both within and outside of the "Harry Potter" franchise, but some of them were still cut from the film.