THe President can veto a bill before it becomes a law. Once a bill becomes law, the President can not changeit. However, at the risk of being impeached, he can refuse to enforce it, or enforce it selectively, enforcing only the parts he likes, the way that Obama treats the Immigration laws.
the power to impeach
he can sign it and make it a law or he can veto it(reject)
Override a veto
If both houses of congress pass it, it goes to the president. If and when he signs it, it becomes law.
The president will veto it
the president sings it.
If both houses of congress vote by 2/3 to override a presidential veto, it automatically becomes law despite the President's veto.
One example of Congress checking the President is through the impeachment process. Congress has the power to impeach the President if they believe he has committed "high crimes and misdemeanors." This allows Congress to hold the President accountable and potentially remove him from office if necessary.
10 days
The U.S. Congress passes bills that become Federal Laws when the U.S. President signs them (although there are cases in which Congress can make a bill into a law without the President's approval), and each state Congress passes bills that become state laws when the Governor of the state signs them.
The Supreme Court rules on the constitutionality of laws. However, the president does not make laws. If he does things that are illegal and not in accordance with the law, then Congress can impeach him for misconduct.
Congress must set its own pay.