There's also an important addition to Congressional power,
made by amendments added after the civil war,
which let Congress legislate to enforce those amendments against the states.
That means sometimes Congress can also legislate
to protect Constitutional rights against the states.
Back to the legislative process.
Once a Bill passes both houses of Congress it goes to the President for
signature or veto.
If the President signs it,
it becomes a law, if he vetoes it, it goes back to Congress.
Congress can override the veto, it can make the Bill a law without
the President's consent if it can get a two-thirds super majority vote
in each house and of course remember the courts are also going to weigh in.
Courts will eventually decide whether the law complies with the constitution or
not and if they think it doesn't, they'll strike it down.
They'll say it can't be enforced.