Players have 4 features that can't be improved using experience points. These are called the "fixed features". Some of them can be improved by special training in the training complex, but takes a long time. The fixed features therefore are an important measure of the potential of a player.
Talent is arguably the most important factor in the long term potential of a player. The higher the talent of a player, the more experience this player will receive every day from the training complex.
Talent has no direct effect on how well a player performs, but a player with high talent will receive more experience points to train his trainable features with. These players will therefore have better trainable features than players with less talent.
Talent has no effect on the amount of experience received from matches.
Like talent, endurance has no direct effect on how well a player performs. A player with high endurance gets tired less quickly. Tired players perform worse in matches and are more likely to get injured.
Endurance becomes very important when your players need to play more than one match a day.
Speed is used for several things in the match engine.
First of all, a player with a lot of speed is more likely to move to another field in the movement phase of a match. The higher the speed, the higher the chance he can make a move.
Secondly, speed adds a small bonus to the blocking and scoring skills of the player. One ball of speed corresponds to 0.1 ball of blocking and scoring.
Power is similarily used for several things in the match engine.
First of all, it is used for long distance passes and shots on goal. A player with a lot of power is more likely to succeed on a long pass or distance shot.
Secondly, power adds a small bonus to the dueling and passing skills of the player. One ball of power corresponds to 0.1 ball of dueling and passing.