A higher youth academy can accommodate and nurture more youngsters, so that your club can get more players coming through from the youth ranks. Your youth academy will produce new youth players at the start of every season, and more youth players will be produced by a youth academy of higher level. A higher youth academy will also develop young talents faster so that they will be ready for professional football at a much younger age.
At the start of every season, new youth players will be available for promotion in your youth academy. The number of youth players and their age will depend on the current level of your academy. The details about how many youth players are generated and their age can be found in the Youth Academy tab under the Club >> Facilities menu. The position of the players generated will be completely random, however if multiple youth players are produced, each player will have a different position. All youth players generated will stay in your youth academy until end of the season, after which they will leave in search of another club.
You can see the list of all youth players available for promotion in Youth Players page which can be accessed through the Transfer >> Youth Players menu. You can then check his details, scout him if needed, and decide whether your club needs his services. You can promote one youth player every season for free, the next one will cost 50% of the player's value, and you have to pay 100% of the player's value for the third promotion.
When the first level of the youth academy is completed, you receive one youth player immediately. And you will continue to receive youth players at the start of every season normally after that.
Youth Player Nationality
In your Youth Players page (Transfer >> Youth Players), there is an option to select the Preferred Nationality of youth players generated. One player coming from your academy every season will be always of that selected nationality, and the rest (if you get multiple players) will be of random Nationality.