With newer versions of Ubuntu (>= 9.10) we can add PPA (Personal Package Archives), a convenient way to get latest versions of software.

To add a ppa

sudo add-apt-repository ppa:<repository-name>/<sub-directory>
sudo add-apt-repository ppa:ubuntu-wine/ppa

You need to have 'python-software-properties' installed. Usually its installed by default. But it's the dependency, just-in-case.

Remove PPA

Install ppa-purge and purge the ppa repository as shown below.

sudo apt-get install ppa-purge
sudo ppa-purge ppa:<repository-name>/<sub-directory>
eg: ppa-purge ppa:ubuntu-wine/ppa

Adding repository or software channel

1. First backup the sources.list

sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup

2. Append the repository links (deb, deb-src) to /etc/apt/sources.list.

# eg:
deb http://in.archive.ubuntu.com/ubuntu/ natty main restricted
deb-src http://in.archive.ubuntu.com/ubuntu/ natty main restricted