What's the difference between anyone and everyone?
- Everyone should keep quiet in the classroom.
- Anyone should keep quiet in the classroom.
Nobody, akin to no and none, means no person at all.
Everybody, akin to every and all, means every one of the people referred to.
Anybody, akin to any, is in between, and refers to any one or more of the people referred to, but not necessarily all of them.
*Anyone should keep quiet in the classroom.
Doesn't really make sense (though we'd likely guess what you meant).
There are statements where they can be used interchangeably:
Everyone who is in the classroom should keep quiet.
Anyone who is in the classroom should keep quiet.
But the two words still mean something different, it's just that both statements logically have the same result; whether we state it by referring to every such person, or any such person.
"Anyone' refers to any person in the room, whereas 'everyone' refers to the whole group, so there is a difference between the two. These types of questions may be better on English language learners: https://ell.stackexchange.com/questions