Using ANTLR to create a grammar.

I need some help using ANTLR to create language grammar. I am just tinkering around with it to see what I can do. I'm just trying to create something simple. I just don't quite understand what tokens are in ERNF. I've checked out almost every website I could, and I think I have a little understanding. Could someone please just try to atleast summarize what tokens are and what they do please?
Thanks!
Shandan