United States Congress
The primary duty of Congress is to write, debate, and pass bills (laws they want).   For Congress to pass a bill, both houses must pass exactly the same bill.  For each house to pass a bill, more than half of its members must vote in favor of passing the bill.  After both houses pass the same bill, this bill is then sent to the President.  If the President agrees the bill should be a law he or she signs the bill within 10 days.  If the president does not agree, then he or she can veto the bill and send it back to Congress.  If the bill is neither signed nor vetoed by the president within 10 days, the bill becomes law anyway if Congress does not adjourn (end its session) within that time.  If Congress adjourns within that time, the bill does not become a law.  Congress may override a president's veto of a bill by having more than two thirds of its members passing the bill.  In that case, the bill becomes law even though the president vetoed it.