After you've added a Newsletter or Document Group to Site Builder, you will see a page which includes the ability to organize the contents of the group, add another document or issue to the group, and edit the group options you originally entered.
Add a New Issue
On the top right you will see a button to "Add a New Issue" to the group. Click it and fill out the short form to upload your file to the group.
Newsletters in Group

Pictured above is a sample of the kind of list you will see once you have added files to your group. This group uses the "Chronological/Or Arrows" sort method. The other option is alphabetical. You can click on any of the Newsletters or Documents to update the file without sending another noticed to your subscribers, if you have any. This list also shows you the date and time the file was last updated.
Newsletter Options

The first section of the Newsletter Options reviews your initial setup of the group, allowing you to make any necessary changes. See the Add a Newsletter or Document Group help page for more information on these options.
The second section of the options box allows you to customize the column headers of the group. If you do not enter anything in these fields, the defaul headers will appear for the group.