Home trained is trained at the club or for two years in your nation under the age of 21(?). That is, a player signed before his 21st birthday becomes home trained once he has been in that country for two seasons.
You also need a certain amount of players who had no previous club (school boys signed on frees with no previous employers or acadamy youngsters).
Finally, remember players under the age of 21 can play in a European game even if they aren't part of the 25-man squad (providing they're not cup-tied, obviously).
However, wrong forum.