Core PHP: User-Defined Functions (6.0)

Functions:

A function is a block of statements that can be used repeatedly in a program.
A function will not execute immediately when a page loads. It will be executed by a call to the function.
A user defined function declaration starts with the word function:

function functionName() {  
   //code to be executed
}

A function name can start with a letter or an underscore, but not with a number or a special symbol.

Function names are NOT case-sensitive.