The followinmg is from O.E. help file and I hope it helps.
To read your messages
After Outlook Express downloads your messages, or after you click the Send/Recv button on the toolbar, you can read messages either in a separate window or in the preview pane.
Click the Inbox icon on either the Outlook bar or the Folders list.
To view the message in the preview pane, click the message in the message list.
To view the message in a separate window, double-click the message in the message list.