Main Pages are just another way of organizing the index page. They allow you to do more things with the right sidebar, like adding a twitter feed and calendar events instead of just images.
To create a Main Page, start with a standard index page. Under System, change the content type from Default to Default Main Page.
Once the content type has been changed, go back to the Content tab and change the Layout to Sidebar.
Now that the page is a Main Page instead of a Standard page, there are many more options in the sidebar. The first is Image, which is the same as it is on any normal page. The next option is Twitter.
To add a Twitter feed, you need to know the Twitter ID and Widget ID of the page you are linking to. For the example, I have used the Cornell College ID numbers, but you may use whatever page you like.
After Twitter is the Facebook option.
To use the Facebook option, go to the Facebook page you want to use and copy the section of text between the word "pages" and the number.
Paste that into the Facebook Page ID section, and you will get a Facebook insert of that page in your sidebar.
The final option we are going to look at is a News List.
A News List is very similar to a Calendar in that they both use Blocks and show a select number of items. To select a News List Block, select Search and got to Browse, where a selection menu will appear. Under "_internal", select "_production", then "Feeds", and finally "news-general" to see a list of available news feeds.
The only other sidebar option for a Main Page is Contact Info. If it is selected, a form will appear for you to fill out with the contact information of the person or group that the page is for. Simply fill out as many areas as you can, and the page will format them into proper contact information.