How to Install Software From Outside Ubuntu’s Software Repositories
 

On Linux, you install software from package management applications like the Ubuntu Software Center. But not every piece of software is available in your Linux distribution’s software repositories.

You should only install software from sources you trust, just like on Windows. Much of this advice also applies to other Linux distributions, so we’ll note what’s Ubuntu-specific and what’s Linux-in-general.

http://www.howtogeek.com/142414/how-...-repositories/