Would someone, for the love of god, please explain to me some things about American elections? I have been told that in Primaries, the PUBLIC cast their vote, choosing directly which Presidential Candidate THEY would like to represent (generally) the party they are affiliated to. However, i also know there are delegates, who then go forward to the National Convention to put forward their vote after the primaries' results. But the delegates can change who they stand for? Are they not just there to represent the public's vote? I really don't quite understand it at all.

I'm aware that makes very little sense.

Help!