Can someone just explain missions to me real quick?
I don't understaaand.

You send a pet away for a set amount of time (1 hour, 2 hours, etc), then you can complete it on your mission page to see if the pet succeeded or failed.

Your level of success depends on how high the pet's stat is in the recommended stat for the specific mission (seen on the upper left corner of the mission pop up screen)

Missions are a great way to make money and build your potion supply, I recommend doing them as much as possible.

Each mission recommends one particular stat, so you want as high as you can get in that stat for successful missions. I'd recommend having a set of sylesti just for missions, and have all their stat points, proficiency points and armor in one particular stat.