Ubuntu includes the convenient Software Center, which provides centralized software management and allows you to search for new software and install it with a mouse click. With an Ubuntu One account, you can purchase software with a credit card.

The Debian packages (that end in .deb ) that Software Center offers are actually archive files containing libraries, configuration files, and executable programs. If you install the Firefox package, for example, the package manager distributes the necessary files to the correct places in the filesystem for you. Often there are dependencies, which means that installing program A requires that you have program B also installed.

The package manager identifies the dependent packages automatically during installation and loads them onto your computer. Usually, you will notice the dependencies when you try to install a single Debian package over the Internet. The package you are looking for, such as a video codec, may be missing in the Software Center. In this case, you can find the package in external repositories created by the software's users or developers. The repositories contain the software as well as the packages on which they depend. (See the "What Are Repositories?" section.)

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