On this page of the Sons of the Forest guide, you will find a list of companions in the game. You will also find out what is their role.
Kelvin is a soldier who survived the helicopter crash. Therefore, he is a starting companion. To make him join you, you have to approach the man and help him. From now on, he will accompany you and follow your orders.
This companion can help you gather resources or build something. If you approach him and press the E key, a list of available commands will appear. This way you will define exactly what he has to do.
Keep in mind that Kelvin is a pacifist. This means that no matter what the situation, he will not fight.
Virginia is a mutated companion that you can control to a lesser degree. You can't give her orders. Additionally, you need to spend some time to make her trust you.
Virginia's appearance is based largely on luck. One day she will start to appear around your camp. Initially, she will run away as soon as you try to get close. But over time, she will become more and more daring. If you hide your weapon when approaching her, the woman will start to trust you and at some point she will bring you small "gifts".
At this point, all you have to do is wait for the option to give her the equipment. Approach her and check regularly if the function has been unlocked. When this happens, you can give her a tracker to see where she is currently. You can also equip her with weapons.
Unlike Kelvin, Virginia will fight cannibals. Therefore, she reduces the chances of your base being destroyed while you are out exploring.