The Assister checks the Monster Live feed and assists where possible. It leaves a message on each monster (e.g. 55th for John), the Facebook news feed (e.g. 55th) and likes the Facebook post.
The amount of stamina, the messages left at monsters and Facebook can be changed in the settings page.

To see what you assisted for you can check the Assister feed. Go to Monster > Live feed. If you already assisted at least one monster (via the Assister) you can see a new tab called Assists. Click and you can see all CTAs you already assisted for.