PHP supports literally hundreds of built-in functions. You've already seen a few, such as echo() and count(). There are many, many more. PHP has functions for formatting strings, searching strings, connecting to many types of databases, reading and writing files, dealing with dates and times, and just about everything in between.
If you ever get the feeling that there might be a built-in function to take care of some task, you should check the PHP manual to see whether such a function already exists. Chances are it does. Definitely check whether your function will manipulate strings or arrays. PHP has a huge library of array- and string-manipulation functions that take care of most common tasks.