Problems with email display. Can't see message body. I moved the box size somehow, and I can't move them back?

All I can see is the Inbox, drafts, sent, spam, trash, and then the next window of Contacts, and last box of folders. Applications in the last box. ALL of these boxes stretch across the screen horizontally. If I click CHECK MAIL or NEW I am unable to see any letter text or the box, it should be in. Can you direct me? It was working well, I think I moved the borders somehow, and my mail box area dissappeared.