Constitutional Law refers to any law which actively deals with all of the fundamental principles, based on which a government is known to exercise its authority. There have also been several instances where these same principles have granted the government specific powers.
A great instance of this would be spending on welfare for the population.
How Does It Work?
All of the judicial, executive, and legislative branches are known to group together for curating, maintaining, and overseeing all the Constitutional laws. They also see to it that these are being maintained by the people as well. The House and Senate both propose and create new forms of federal laws. After forming, the President or the concerned reviews them and gives their approval.
Then in turn, the Judicial branch (including the Supreme Court and all other federal courts) both see to it that the laws are being upheld by the people. They then establish and apply them to cases that occur in the future.
All in all, Constitutional Laws are really important as they protect the rights of various individuals like you and me.