A plan of government is called a constitution. For example, the Constitution of the United States of America lays out the system by which the U.S. government operates, such as the three branches of government, voting rights and the rights of states.
The U.S. Bill of Rights is not part of America's plan of government. Rather, it is a charter, or code of citizen's rights and liberties, included as an addendum to the original U.S. Constitution. The Founding Fathers believed it was important to ensure that American citizens were protected from their new government's power, so they insisted on including a charter as part of the Constitution, building these rights into the structure of America's federal government plan.