"учитель" = "teacher". "читатель" = "reader". I still mix them up, too. We need some kind of mnemonic. Maybe imagine a teacher telling a student, "you cheated on the test." "You cheat" > "у чит" > "учитель". Goofy, I know, but if it works, who cares? (Now, what does a cheetah have to do with a reader? lol)
It can mean a person who reads aloud to others, like the lady at the library who reads stories to kids, or a person in church who reads the bible to the congregation. It can also mean a person who reads books, newspapers or the like; I am a regular reader of the Allentown Morning Call. It can also mean a book of short stories used by children learning to read.