Morgana,
It really depends on the sleeve pattern. Most sleeve patterns have a default length that is mentioned in the description. If you want to change the length, there is a Sleeve Length variable option when drafting.
If you leave that variable to 0, then the sleeve will draft to its default length. If you want something different, you would enter the length you want measuring from the shoulder point down the arm.
Variables are a more advanced topic and you might want to play around with default drafts until you get the hang of it. You can output to PNG to see the patterns without printing or export them to the Fashioner to look at them.
You might want to take a few moments and review the manual for Patternmaker Pro which has lots of information about the system. That is available from the Learn option on the main menu.