New to Blackberry question

I am new to Blackberry's and I was wondering if someone can answer a few
questions for me.

1) With e-mail. If you are accessing a IMAP account is there a way to
see other folders in the account? the inbox is nice but I filter mail on
the server.

2) What is Blackberry Messenger?

3) What are browser messages and WAP pushes

That's a start

Thank you

TC