How did Karana capture the leader?
I think that you must be talking about the leader of the wild dogs, not the leader of any group of humans. This happens pretty near to the start of Chapter 15.
What Karana does is she smokes the dogs out of their lair. She starts a fire going and when the dogs come out of the cave because of the smoke, she starts shooting them with her bow and arrow. She gets the leader.
Later on, she comes across the leader, who is near death. She takes him home and nurses him back to health. By the time he is well, he is tame.
check Approved by eNotes Editorial