EAP 5.1.x is based on JBoss AS 5.1.x, so all of the AS documentation should apply. See: http://www.jboss.org/jbossas/docs/5-x But realize that unlike AS which is unsecure by default, EAP comes secure out-of-the-box. So you will have to immediately deal with security issues. For playing around, you might want to use AS 5.1.0.GA.
And if you are a real beginner, grab the free chapter 1 from JBoss in Action (link below); it'll get you started.