Well, imagine a group of people playing a game together. They need someone to be the leader, or the "captain," to help organize and make decisions for their team.
Now, a really long time ago, a country called Portugal claimed a big piece of land called Brazil. They decided to split Brazil into smaller parts called "captaincies." Each captaincy was like a team, and they needed someone to be the captain or leader of that team.
Each captaincy was ruled by a captain who had a lot of power over his "team." They were responsible for making important decisions, like how to use the land for farming or where to build settlements.
Over time, Brazil changed a lot. The captaincies were no longer the same as they were in the beginning, and some of them even became states. But, the idea of having leaders or "captains" to make important decisions still remains in many parts of the country today.