The bill first starts in the House of Representatives. Where it is given a HR number. Then it goes through all of the House's committees. After that the Bill is discussed and if it's passed it is sent to the Senate.
The Senate goes over the same process that the House did. The senator addresses the bill and then it gets a number and is sent to the senate committees. If the Senate passes the law and the House then it's sent to the President.
THE WHITE HOUSE
Once both the Senate and House agree on the bill they send it to the President. The President can do two things Veto it or Sign it. Signing it means it can be passed and it will become a law. Vetoing it means it won't be a law and it will go back to The House and start over agian unless it's overriden.