Any bill can start in any house. Theoretically, they both can start bills and pass them to the other house. Though, the senate is usually the one who limits the bills and thrills them back to the house.
Then the house must modify it again so that the Senate has no problem with it, and then they pass it to the president
THe president can either sign it and the bill becomes law or the president can sanction it and send it back to congress
hope it helps