I believe the answer is:
- A committee reviews the bill and marks it up to make it more viable and to reflect interests of committee members.
(During this process Committee members would gather together and conducted a debate on the cost and benefit of the bill in order to determine whether the bill should be passed to the next level)
An idea for a law is drafted by someone interested in seeing a law made who then finds a Congressional sponsor to back it.
(when congressional sponsor decide to back it, they would give their vote count for the bill and the bill would be actualized if it managed to obtain a total backer of 2/3 from total amount of congress)