Exactly as DiZZee say, you just have to go to your friends team and if they are in your server, you click under the player, and you will see a place that say; make an offer.

Actually, I am in my 14th season and I have my 4th Goalkeeper, well.. have to start looking for the 5th....-.-' (I like this position a lot, because I was fan of oliver Kahn) and, to obtain my actual GK, called Songo'o (GK of Deportivo de la Coruña when they won the league 15 years ago) I did an offer of the 50% more of his value.
His value was 18M and my offer was of 27M for a 5* GK that need only 1 skill point for the 6*... but his team was of same level as me, and thats why I did a high offer,, so, in the case of the 2* youngers that recive a better team 3 levels under you from the academy, will be more easy the deal.
Too in future, with the academy at max, you will recive 2 players from every 12 days, and the player of 4-5* in my case, is always interesting.
yeah, they cost 24 tokens, but, train fast, and in my case are very efective and loyal, so that's a 2nd option.