Hi! Expertise is like a rating for how useful an NPC is. They start at Expertise 1 unless stated otherwise.
When you decide that your character gets a hired gun, you roll for their class (with a d8), or choose the most fitting class. If you roll an 8 they start at Expertise 2, and so on.
They don't have any stats except Expertise which is the value of the bonus they give you. They don't have HP either, but instead die when taking 3+ damage on a single hit.
For example, let's say you have a hacker buddy with Expertise 1. Three times a day, they can provide you +1 on a Knowledge test, and use a random app once a day.
If they live long enough (which they shouldn't), you can have them GET::BETTER() and increase their Expertise by 1 if you want to.