Ubuntu's software package installation uses a list of repositories that house the various updates and software that you can install. By default, the repository list doesn't include a lot of the 3rd party tools that you might want to install.

Most of the instructions for adding extra repositories tell you how to use the command line tool, but for new Ubuntu users, a GUI tool is probably more useful.

Ubuntu Edgy includes a software tool that lets you manage these repositories easily. You can find the tool on the System \ Administration \ Software Sources menu.

When you launch the tool, you'll be presented with a dialog that allows you to easily check the boxes, or even change your download location from the default of US repositories:

For most publicly available software, you'll want to enable the universe repository. If you navigate to the other tabs you can also choose how often the automatic updates feature checks for new updates.

Tested on: Ubuntu Edgy Eft