The cable cast on can be used at the beginning of any project in place of other basic cast ons. But the reason it's special is that you can also use this cast on in the middle of a project: at the beginnings of rows and in the middle of them, too.
It's very similar to the Knit On Cast On, except that instead of knitting into the next stitch on your needle, with the cable cast on you knit in between the next two stitches on your needle.
If you haven't already, familiarize yourself with the different styles of knitting before continuing. There are three different ways to hold your yarn when knitting and you want to make sure you're watching the right technique for you.