What does article 1, section 7 of the constitution explain

When both the House and Senate approve a bill, it then goes to the president. If the president approves, the bill becomes law. If he does nothing for ten days, it automatically becomes law. 

The president can also veto. It's then send back to for reconsideration. If he vetoes, the bill must pass again with a 2/3 vote. 

Congress, however, has the power to override a veto.