NAH I KNOW THIS
It is legislative, executive, and judicial.
The legislative branch (congress) must have the president sign a bill whenever they vote on a law. The president can veto or sign it. The congress has the ability to override the veto but that rarely happens. For the executive branch (military, president) they must have the okay of the congress and the senate before they do anything big, like declaring war for example. For Judicial (Supreme Court, lower courts) they have the ability to declare laws unconstitutional. So if a bill passed by the legislative branch is deemed unconstitutional, they have the ability to strike that law down. Checks and balances exist so one branch doesn't have too much power and become "tyrannical".
I can't believe you had to ask for this. You should start studying and be grateful for the liberties this country gives us, lil bro.