Actually it's not a function and it's not really System.out.println();
There is the System class, which represents the computer you are using. It has a
static field called
out, which is a PrintStream. So when you write System.out, you get your hands on
out which you can find a bit more about
here.
If you look up System.out, as I said, you find it is a PrintStream, and that link tells you it is println methods. You can click on those and find out more details. Alternatively, you can click one of the underlined PrintStream links, and you find lots more about it, and other methods you can use. So it's not simply System.out.println(). It's three things:
get the System class.Get its "out" field.Get that to use its "println" method.
. . . and welcome to the Ranch