There are, I think, many threads concerning this topic, and concerning what happened to Beleriand. Here are two:
Where is . . .?
and .. .
Sinking Beleriand .
Reading the Silmarillion would give answers to your questions.
You could also check out this, which is a simple and short explanation concerning Beleriand:
Where in Middle-earth was Beleriand.
Nova
__________________
Scully: Homer, we're going to ask you a few simple yes or no questions. Do you understand?
Homer: Yes. (Lie dectector blows up)