Im trying to transfer too, and here is what I've gathered.
1) What is the GPA
-Grade Point Average. Almost every University uses this if you wish to transfer from another uni to another.
2) How does it work?
Its different at every uni but generally, each grade you get for each subject is assigned a point. The higher grades you get, the higher points you'll have.
e.g HD = 5
D = 4
They add up all the scores you got from each subject you've done and then they divide it by how many contact hours to get your GPA.
3)So what about the different GPA's you were talking about?
Different uni's use slightly different modifications of the GPA. generally, they might use diffrent SCALES. So for a five point scale, a HD might equal 5 and a fail equals to 0, whereas a 7 point scale, a HD might equal 7 while a fail might equal 0,1,2,3 depending on how badly you fail.
4)So then what GPA do I need to transfer?
Depends, but they award places to the applicants with the highest GPA's. And to apply you also need a minimum GPA of a credit (varies with uni's)