Setting a Default, or Landing Page
This How-to applies to: 2.1, 2.5
Let's say you've created a folder and then a few pages within that folder. One of those pages you intend to use at the landing page, or page people see when they click on the folder (remember that folders are often also navigation buttons).
In older versions of Plone, you had to change the Short Name to index_html. Now Plone gives you a quicker way of doing the same thing. Note: Short Names are still used in Plone and must be dealt with when renaming content items. Please see the renaming guide for help in properly renaming items.
To pick a landing page, also called a default document, you must be viewing a folder. Then click on the Display tab found in the green task bar.

From here you can actually choose several different ways to display folder contents, but for the default document click on select a content item as default view . . . (highlighted in red). You'll then see a listing of all content items in that folder and you can choose whichever one you need.