This question was asked quite frequently. The short answer is to hire and coach and assign him to a member of your team! For a longer explanation make sure to check other posts :)
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You need to hier coach/trainer. Then you go to "Players" you click specific player, you can see this http://i.imgur.com/a4xuf1n.png . Each action such as playing one team ranked, playing a solo queue game or having a session with a trainer takes 1 unit. The positional skills (ad carry, top, mid, support and jungle speak for themselves. How good will they be at specific roles. Teamwork right now is used for teamfights however this is bound to change and be more overall type of skill. Technical skill affects last hitting only right now.