Software in Linux comes in two main forms: this article covers only the easiest way of installing software.
If possible, you should always install software directly from the Repositories. The Repositories contain software already packaged for your One, complete with things like menu entries and so on. If the software needs other software in order to run, this too will automatically be installed at the same time.
The One uses a graphical tool called Pirut to install software. Once you have enabled the right-click menus, you will find this on the menu under System -> Add/Remove Software. Click it.
The system then asks for your password. Linux will not install anything without your permission, and always asks for your password. Enter your password and click OK.
Now Pirut will load the list of available software - be patient: even once the progress bar disappears it will take a little while to display. There are three tabs: we'll concentrate on the first two.
In the Browse tab, you'll find categories of software. Click on (for example) Applications, then on Games and Entertainment in the right hand panel. After a delay, a description of this type of software will appear, together with an 'optional packages' button. Click on this button, and you will see a list of lots of games you could install. This is just an example to let you see how the Browse system works - if you are looking for software of a particular type but don't know exactly what you are after, use this approach.
This is pretty obvious, really: put the name of the software you want into the box and click Search. Then select from the list which is produced.
Completing the InstallationEdit
To install something, tick the box by its name, and click 'Apply' - the system will then check whether it needs to install any additional packages (dependencies) and check with you that it's OK to do so, and then download what it needs and do the installation for you. When it finishes, close Pirut, then you'll find your new software on the right-click menu (unless it's something you can only use from the command line).