Utilities provide user-interface functions that are basic to the modern concept of an operating system but which are too complex to be built into the shell (remeber that small and focussed is better in the UNIX philosophy).
There are usually over 300 such utilities built in to the UNIX systems shipped today and we will discuss many of them in this tutorial.
Of course, you can also install larger utilities such as commercial software packages, but those are usually considered separate from the UNIX OS whereas the built-in utiities tend to get clumped into the OS since they they are built in and the difference between them, the shell, and the kernel is transparent to the user.
So the next question must be how do you use these utilities? Well to answer that we return to the shell.