how do I close the right side message view in mail

Here's how I do that in Yosemite (OS X 10.10) -

Open Mail. Open Mail's Preferences (in the Mail menu in the main menubar). On Mail's Preferences, go to the Viewing tab.

Click (checkmark) the item "Use classic layout". That should change the layout of the window to the old-style over-under arrangement for the mail list and display panes. Then drag the dot in the center divider (the horizontal bar that separates the message list pane from the message display pane) all the way to the bottom of the window so that the bottom pane is closed.

Uncheck the item "Use classic layout". That should result in the 'new' style layout but with only two panes showing - the mailboxes list (if set to show) and the list of messages. The display message window should not be open at this point. If you wish to re-open it, look for a small dot in the right-hand margin of the window, and drag that dot a bit to the left.