Yes,the title of the post is giving you the right information.Gmail has added a new option named "Preview Pane" to give a better and details view to the users of the Gmail.This is noted that this concept is not a new one and you have already seen it in some customized mail like Outlook Express but the new option will make the view of the interface more details and specific this can be said undoubtedly.Below are the steps to enable this in your Gmail:
1.Go to the "Labels" and click on "Manage Labels"
2.Then Click on "Labs"
3.Then you will get the option "Preview Pane" and Enable it.
4.Now save the changes
5.Now go to the Gmail Interface and click on the Split option on the top right hand corner of the surface and select as you like.
Now you are done.
Enjoy the new look!