First I'm not very familiar with lower league clubs and I'm more like guessing here.
Do you have a youth academy? With the big clubs who all have their own academies you get a message (in March usually) to take a look at some of the academy graduates who are on trial with your youth team. You then have to offer them contracts during the trial period to sign them.
But if a club doesn't have an academy then they perhaps have to sign youth players from other clubs...?