Your damage is split into two categories: Physical and magical.
For the most part, magical damage is by using x, for the exception of elsword which X is just a stronger swing.
All z attacks are physical.
Dame of skill is dependent on their percentages.
For example, if your attack power is 5,000, and the percentage is 1,000%, you'd do 50,000 damage.
Percentages vary, a really huge number like 1000% means that it's a one shot move, or at least a very limited number of hits.
Small percentages means several hits.
Such as windmill's percentage is only at 93%, however it does 43 hits in awakening mode.