Function e: vs. event

Question

I'm a actionscript / flash noob and had a question about flash.
I've seen different functions written different ways but one thing I don't understand is the "e"
for example.
function name(e:MouseEvent):void {
and
function navOutF(event:MouseEvent):void {
I had thought that "e:" was shorthand for 'event:', but when I tryed to used them interchangeablly (replacing 'event' with 'e:'), the script would could back with errors. And so now I have no idea what it means, and when to use e: and when to use event.
Also, if someone could tell me why I have to put ':void' after each function, that would be helpful...

Answer 1

Ok, for theory sake (forget events for now) say you have a function that accepts two arguments e and event:
function myFunction(e:int, event:String):void{
     trace(e + " :: " + event);
and you call the function like this:
myFunction (3, "aha");
the trace will be:
3 :: aha
Now, say I change the function:
function myFunction(foofoo:int, booboo:String):void{
     trace(foofoo + " :: " + booboo);
you still can use the function exactly the same way:
myFunction (3, "aha");
and the trace will be the same
3 :: aha
With events you say that a function will be called and an INSTANCE of Event will be passed into it. IT DOESN"T MATTER what name you give to the arguments as long as the datatype is some Event. It can be e, event, hisMother, etc. But if you say that the name of the argument is "event" - you have to refer to this argument by name event - not e.