Path of Evil has two types of ways you can team with your companions. Here is an example of each.
A particular companion is in the party: Your companions have particular skills that you can access by asking them. One companion is a skilled forger for instance. So in a quest involving forgery, if the companion is in the party you can simply ask them to do it. You can try your hand at forgery yourself if you'd like, but there are skill checks involved. The companion automatically succeeds.
This type of teamwork requires you be able to talk to the companion, typically without anyone who would find the action hostile being there to notice. You can't have your companion forge something if the NPC's are standing there.
Friendship teamwork: The companion Kvas is your best friend from childhood. Because of this, you have teamwork options with him that you can carry out even if you're being watched. For example, you can distract someone while Kvas steals from them.
Friendship teamwork involves a skillcheck, but not one for the action being attempted, rather it's a check to see if you distracted the NPC sufficiently for Kvas to perform an action. For example, there is a quest that involves putting poison in someone's drink. You can try this yourself with a sleight of hand or Dexterity check. If Kvas is in the party, you can check Craft Weapon and make small talk about the NPC's scimitar, or try a Perform check and sing a quick song in the NPC's honor. A successful check distracts the NPC enough for Kvas to put the poison in the drink. Kvas's success is dependent on your skill.