Cohorts, Followers, and Hirelings
Cohorts and Followers may be obtained only by taking the Leadership feat. These will be created in concert with the DM. They earn experience per the rules on page 129 of the CRB.
Hirelings may be acquired by anyone. This just requires the character to find someone they wish to hire, and make them an offer. This character will have an NPC class and a number of levels assigned by the Dungeon Master at the time they are hired. Hirelings will only fight to defend themselves, except for warriors who will fight to defend themselves, or the person/property of their employer. Most hirelings will provide assistance in circumstances and will even help their employer who has fallen in combat, but only if doing so does not put them at risk. Unless ordered otherwise, non-warrior hirelings will withdraw from combat if threatened.
Hirelings are also created with the DM. Hirelings gain ½ the experience the PC receives, only for encounters in which the hireling participates. They do not receive experience for Role Playing or Creative Thinking. The higher the level of the hireling, the more gold he will charge. Hirelings subjected to extreme risk or who are underpaid may desert. Some might require hazard pay and contracts ensuring their resurrection (or benefits for their families) if slain. Additionally, they might become unfriendly, but a player character can potentially influence them to a better attitude and perhaps even talk them out of hazard pay, etc. through role playing and Diplomacy skill checks.
Cohorts and warrior hirelings will use separate initiative scores. Followers and non-warrior hirelings will act directly after the PC who controls them.