The two areas you should get familiar with first are the "Lessons" and "Practice" sections. In the Lessons section you can view Vocab/Kanji lists, and take tests sectioned by chapter. The Practice section drills randomly selected Vocab and Kanji from the chapter you're working on.
I would sugest you take the tour aswell. from the home page below the main page tabs but before 'recent echo' there is a little tab that says "Introduction" if you click that at the botom of the section it says "take a tour" this goes through all the main functions of the site and has screen prints etc.