A captain is the person in charge of a group. The captain of a high school soccer team is usually an elected or appointed leader.
The word captain can describe any leader, but it's traditionally been the name for the person on a boat or ship with the highest rank. The captain of a fishing boat is responsible for making decisions about what route to take and how best to avoid bad weather. When she steers the boat, you can say she captains it. The word comes from the Late Latin capitaneus, "chief," from caput, or "head."