A function contains code that will be executed by an event or by a call to that function. You can however use a function to contain the script and call it every time your need it. Here is the syntax for a function.

Syntax:
 function name (parameters){
   statements

   }
The function keyword identifies this as a function. The parameters in the parenthesis ( ) provide a means of passing values to the function. There can be as many parameters separated by commas as you need. It is perfectly ok to have a function with no parameters. These parameters are variables which are used by the JavaScript statements inside the curly braces { }. The var keyword is not needed to declare the parameters in a function as variables because they are automatically declared and initialized when the function is called. The function can return a value by using the return keyword.

You should put your functions in the HEAD section of your document. Functions will work if you put them in the BODY section. However, a function must be loaded prior to the statement that calls it. Putting all functions in the HEAD section is the way to insure this.

Example:
 function myAdder (num1, num2){
   var total = num1 + num2
   document.write(total)
   }

You would place this function inside some tags in the head section. You then can call the function from anywhere in your document. In this example, lets call it from within some tags in the body of document like this.