The Desktop Environment (DE) is what makes up most of the user interface. It may include system panels, docks, window borders, backgrounds, and desktop widgets, among other things. GNU/Linux has a wide variety of DEs avaliable—this page will outline some of the most popular ones.
GNOME is touch-friendly desktop environment that aims to be simple to use while still offering a full set of features that appeal to advanced users. If it appears to be missing a feature, you can probably find it in the extensions database.