Congress Passes A Law. But How Can It Be Checked..the Supreme Court May What?

Once Congress has passed a law in both houses, it has to go to the President for approval or a veto.  If he vetoes the bill it can be sent back to Congress and can be overridden with enough votes.  Once the President has signed a bill, it becomes law.  

When a bill becomes law, it doesn't go to the Supreme Court unless it's challenged in a lower court.  Even at that point it doesn't automatically end up in the Supreme Court.  The validity of the law in relation to the Constitution and existing laws has to be evaluated through the judicial branch of the government.  The courts may strike down the challenge or it can pass all the way to the Supreme Court.  If they choose to hear the case, the justices will eventually deliver their opinions.  At that point, the law can be upheld or declared unconstitutional.  It's a long process that could even take years to be resolved.