Choose a distribution
Because there is no "one GNU/Linux", finding what you need can be difficult. Here are our choice of three beginner-friendly, widely used distributions.
Note: There are plenty of distributions to choose from and compare.
This is our selection for newcomers. These links are not commercial.

Simple, easy, usable and our personal favourite. A tanned, smooth atmosphere that never gets in your way. All programs are kept in order and managed easily. Configuration is kept simple rather than exhaustive.
We recommend this friendly and complete distribution if you are looking for an easy way to try and step into GNU/Linux.
Ubuntu also has a sister distribution, Kubuntu, with a different layout and slightly more advanced graphics.

The distribution by the long-time prominent GNU/Linux developer company Red Hat. The default layout is similar to Ubuntu (it is also possible to use KDE, the more advanced desktop environment in use in Kubuntu), but there are differences in the chosen applications, install protocols and several technical elements.
We recommend this distribution if you wish to learn more about the workings of a GNU/Linux system, security configuration, or work on software development.

Since Ubuntu contains some restricting components (why?), the Trisquel developers have built an entirely free derivative. Although its community is smaller and its hardware support might be slightly inferior, Trisquel gives anyone full freedom over a complete operating system similar to Ubuntu.
We recommend this distribution if you are committed to freedom in your computing.