do players from youth system perform better?

[Tactician]

Can u tell me how to train him to a desired quality with green packs?

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Go to training section and train the player with appropriate drills (or those that will boost the attributes you want). Recover the condition of the player using green packs if needed. If not, do another training session. Repeat the procedure till you achieved the desired quality.
Manage your expenditure of green packs to make the most out of every green pack used though; that is, recover a player's condition when it has 84% or less condition as a green pack provides 15% condition recovery. Drills at higher levels will have better efficiency; for example a drill at 3 whistles will give more gain in quality for the same amount of condition spent as compared to the same drill at 1 whistle.