Ability's consist of meeting certain requirements while on the battlefield, each character is different in terms of 1 character could have 3 ability's to obtain while another could have 4 or I think 5. You can check a characters ability on the battle prep by going into team info, choose character then ability.
RecommendedLevels for Ability's/Proficiency:
Wu - Stage 4 Battle of Itskushima (EASY MODE)
Shu - Stage 3 Battle of Nagashino (EASY MODE)
Building your Proficiency
If you would like to keep track of your progress use of the following excel spread sheet to keep track.
Proficiency Record Table