Youth players can focus on two types of training at the same time, one primary and one secondary.The primary training has more effect than the secondary. You can choose to train the same thing (for example defending) as both primary and secondary training, but the training effect will be bigger if you choose two different training types.
Youth players receive training from both league games (full effect) and friendly games (smaller effect), so they can receive training twice the same week. You need to give your training instructions before the game starts. The effect of training appears after the game is finished - 24 hours later your trainer will give you a report about what has happened in the team, with a lot of good hints about the players' progress. You may also get the chance to reveal skills:
For your primary skill training, your coach will inform you about the current skill level for one player who's played at least 44 min in a trainable position (i.e. receiving more than very small effects). The same goes for your secondary skill training, but in this case he will inform you about the maximum potential in that skill instead of the current level.
Note that you do not receive a report for the secondary training if you train the same scheme as the primary training. If all players in a trainable position have had their skills revealed, your coach is naturally not able to give you a report of this kind. Also, if you have fewer than 8 players on the pitch when the match ends, you will not get any skills revealed.
Additionally, your coach will normally report one of the three players with the most potential (highest maximum skill level) in a non-trained skill.