MAIL LAYOUT

Usually whenever I would open the mail app, it would give me three columns, the first (far left) would have the emails id want to access, flagged, inbox, draft buttons - the middle column would show all the inboxes of whatever I pressed on and then the third would be the actual message that I would click on with my cursor. But I mistakenly pressed the wrong button that no longer shows me the message of whatever my cursor is on & what I hit. below is a picture of how id like my screen to look. I want to be able to view my mail messages without having to double click and then my message appear on a different window, Im just not sure where thats at :( pls help the 2nd picture is how my mail currently looks, I just want to be able to view my messages on the far right of the same window.