Best thins is to check out the help files on Functions found here,
http://www.autohotkey.com/docs/Functions.htm
Basically functions are similar to sub-routines.
If you don't know what a sub-routine, try starting there as they can often be easier and make a good intro to Functions.
Check out sub-routines here
http://www.autohotkey.com/docs/commands/Gosub.htm
To summarize both functions and sub-routines in general terms:
You can think of either as a specified job / calculation like boiling a kettle for example.
A "call" to a function is a command in a script that initiates that function ie someone shouting "please boil the kettle".
Sub routines work similarly but as i said they can be simpler to understand or tat least the help file is
g543 wrote:
Welcome to the board. Plese fasten your seatbelts.

What for? This has to be the slowest forum I have ever seen.
And its unhelpful smart ass comments like yours that grind people's progress to a disgruntled halt,right before they completely give up on the forum and AHK.