Using the preview pane

The preview pane makes it so that you can view a message without opening it fully - it is what makes Outlook appealing to many users. In order to utilize this function, you have to Enable it.

Open your Gmail Settings
On the Labs tab, scroll down to Preview Pane and click Enable.
Click Save Changes.
Gmail will reload. Once it reloads, you will see a new button called Toggle split pane mode to the left of Settings.
You can choose between No Split, Vertical Split (like Outlook), or Horizontal Split