A capitol building (or just capitol) is a building in a capital city. People who control government work there to make laws. The building may have many offices.
Some offices are for legislators, the people who make the laws.
Some offices are for people who enforce laws, for example a president or governor. These people lead all people, and help them obey the laws.
Sometimes, there are offices for judges, people who help all people understand the laws. These judges are very powerful. A group of these judges can be called a supreme court or superior court.
Buildings similar to capitols are in other places. A smaller government like one in a county can be in a court house. A city government can be in a city hall.