Commission is the section of the Association where you complete chapter levels, just like in the Love Nikki story! Every member gets to do 5 tries for free every day. Those tries can be all on the same level or on different levels. The difference between the story levels and the ones here is that contributing to these levels gets different benefits.
The benefits to doing your guild commission levels are
-5 Association coins per completed attempt
-"Currency" in the form of hairpins, necklaces, and earrings (used in the Workshop)
-2 Activity points per completed attempt
-Unlock suits in the Workshop by completing the chapters
Doing your Commission attempts is the main way to increase your activity within the Association.
If you do all 5 free attempts, it will get you 10 activity points every day. You can get even more activity points (as well as the other benefits listed above) if you purchase more attempts for diamonds.
You will gain some Workshop currencies for each attempt, as well as a bonus amount for completing a stage.
You may have heard people say Chapter 6 is the best one to do after you've unlocked all the Workshop suits. This is because Chapter 6 is the one that most people score the highest on. What this means is that you will finish the stages faster (since they complete at a specific number of points reached), and you will receive those Workshop currencies faster because of it.