There is wide variety of subjects being taught at Hogwarts, but some of the main ones that are commonly mentioned in the books are:
IMPROVEMENT:
In first and second year there are only 6 subjects taught then in third year you get a choice of 10 subjects. There is 1 subject taught during the first year only. I have also included the teachers I know =]
Subjects taught during first and second year:
Subjects taught in third year (please note there are 10 subjects taught in 3rd year but I've found 11 - I'm not sure which one of these isn't in 3rd year - sorry):
Students have to select some of these subjects and not even clever clogs Hermione can study all 10 =P
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Herbology was taught by Professor Pomona Sprout.
First year students take flying lessons which is taught my Madam Hooch.Students are required to take the following class in their first five years at Hogwarts:Transfiguration taught by Professor McGongallCharms taught by Professor FlitwickHerbology taught by Professor SproutPotions taught by Professor SnapeHistory of Magic taught by Professor BinnsAstronomy taught by Professor SinistraDefence Against the Dark Arts taught by Professor Qurriel (first year), Professor Lockhart (second year), Professor Lupin (third year), Fake Professor Moody i.e Barty Crouch jr (fourth year) and Professor Umbridge (fifth year).In third to fifth year along with the subjects listed above Harry Potter studied:Divination taught by Professor TrewlaneyCare of Magical Creatures taught by Professor HagridIn sixth year students are allowed to drop and choose whatever subjects they please. Harry took the following subjects in sixth year (and seventh had he returned for it):Potions taught by Professor SlughornCharmsDefence Against the Dark Arts taught by Professor Snape (sixth year), Professor Carrow (seventh year, turned into 'Dark Arts')TransfigurationHerbology
Transfiguration was taught by Professor Albus Dumbledore. When he became headmaster he was replaced by Professor Minerva McGonagall.
Remus Lupin taught Defense Against the Dark Arts.
The spell that opens a locked door is "Alohomora!" The spell is taught during the first year of education at Hogwarts. The first book in the Harry Potter series -- Harry Potter and the Sorcerer's Stone -- chronicles Harry's first year. "Alohomora" is a charm and thus would've been taught by Filius Flitwick during Harry Potter's time at Hogwarts.