Here is a quick way to install Mixxx, Mixxx is free open source DJ software that gives you everything you need to perform live mixes.
To install Mixxx open your Ubuntu Software Center (Applications -> Ubuntu Software Center) and type: mixxx in the search field. Select Mixxx and click the Install button, fill in your password and wait for the installation to finish. When installed you can find Mixxx under Applications -> Sound & Video -> Mixxx
Enjoy your mixing 🙂