You can acquire a new player each week by sending your scouts out to find a new player for the senior squad. The better the scouting network is, the better the chances of the scout succeeding. You don't have any options on what kind of player you'll get, apart from choosing between a goalkeeper or an outfield player. Don't count on receiving top notch players each week. Most players the scouts recommend won't even be suitable for the reserve team. If you have one or two of them moving directly up into the team you should be satisfied - think about how things work in reality!
Most clubs put a lot of money into their scouting network, but there are also those who spend less money or none at all, buying reinforcements from the transfer market instead. However, if you do decide to build up your scouting infrastructure, be prepared that it might take some time before your investment pays off with reasonably able players. You may find there's little point in using the network if your scouting network status is "poor", for instance.
Every week you're allowed to make a large (13 333 £), medium (6 667 £), or small (3 333 £) investment into your scouting network. Many small investments are more efficient than a few large ones. In other words, it's wise to make long term plans - if you're willing to invest a lot of future funds into increasing scouting activity, large investments can be a way to get results quickly. If you want to build up a decent structure gradually, without spending too much money, make a small investment each week. The upkeep of the scouting network won't automatically cost you anything, but if you don't make sure of regular funding, the structure will deteriorate quite rapidly. Once the level of the scouting network has dropped, it will take a long time to raise again.
You're only able to promote one young player per week. If you don't change the amount, the amount invested the previous week will be used.
It'll cost the club 1 333 £ to promote a junior.
Information on your youth squad activities can be found in the "My Club" menu, under the "Youth team" header. This is also where you enter the amount of money you want invested into the scouting network, and where you can find a player using the network each week.