Short Version:
Each character gets 3 starter JP, that they can spend to learn already created jutsus.
Then, you can receive JP only by leveling up.
1-5 level receives 2 JP per level up.
6-10 level receives 3 JP per level up.
11-15 level receives 4 JP per level up.
15-30 level receives 5 JP per level up.
31-49 level receives 6 JP per level up.
50 and above level receives 7 JP per level up.
To learn..
Rank E, you need 1 JP
Rank D, you need 2 JP
Rank C, you need 3 JP
Rank B, you need 4 JP
Rank A, you need 5 JP
Rank S, you need 6 JP
Rank SS, you need 7 JP
If player has enough JP, he can go to a certain teacher. The Teacher will give a mission, witch will require retrieving a scroll. After the scroll is brought, you will receive the jutsu.