As a citizen, if you wanted to propose your idea as a bill you would present your idea to a legislator, so (in the US) a Representative or a Senator. Members of the legislative body are those who propose bills in committees where they are discussed, amended, and voted upon. Next, the bill moves to one floor of Congress and, if it receives enough votes, moves to the other. After both halls of Congress have approved the same bill, it moves to the President who can either sign it or veto it.
