How to add repositories to your ubuntu

Because of that default repositories don't contain the right locations for most software packages that you'll want to install, you need always to add a repository to your ubuntu installation, to be able to download and install packages.
How to add new repositories?
You will want to open up the /etc/apt/sources.list file, find and uncomment the following lines
Repositories on Ubuntu are the locations that you can download software from. As a general rule, the default repositories don't contain the right locations for most software packages that you'll want to install. You will want to open up the /etc/apt/sources.list file, find and uncomment the following lines

deb http://us.archive.ubuntu.com/ubuntu dapper universe main restricted universe

deb http://security.ubuntu.com/ubuntu dapper-security universe

Note that if you are using a different version than Dapper Drake (6.06), you will probably see a different name there, something like breezy or edgy.

Once you are done adding the repositories, you'll need to run this command:

sudo apt-get update