You'll find most of your answers in the links of this Thread:
http://forum.topeleven.com/tutorials...ls-guides.html
It contains several tutorials made by users.
By training and playing games your players gain XP points. Everytime your players gain 100 xp points, they get a Skill point. You assign the players skill points to defence/attack/Physical. Your players Average quality is exactly an average of these 3.
As to stars, a player will gain 1 star each time it's AQ raises to a multiple of 5. a players with 25 AQ has 1 more star than a player with a 20 AQ, and 2 more stars than a player with 15 AQ.
The number of stars actually depends on the level you're at. Level 1, a player has 3 stars at 10AQ, 4 at 15AQ and 5 at 20AQ. Level 2, 3 stars at 15AQ, 4 at 20AQ, 5 at 25AQ, and so on...
For a more detailed explanation please refer to the link above.