With Skill Posters come Skills! These aren't entirely unlocked through the Coin Bingo of PW2 or from getting specific coin combinations in PW1. Instead, once you get a Skill Poster, you must refer to them in order to get the Skill by either using the specific character and doing what it requests of you (such as Zoro's Skill 1 requiring you to defeat one tough enemy) or unlocking it through successfully achieving the requirement (like, I think it's Alvida's that requires you beat her down once in order to unlock her first skill from her poster).
Chances are this will probably come rather early on if you stick to one character (I kept with Luffy and unlocked it through killing so many soldiers per map). His first Skill requires you to get 300 "!" (read as Beat) in one battle as him. This can come from killing enemies in Kizuna Rush as well as kills from special attacks.