Stage 1: The Bill is Drafted
Legislation can be written by anyone, but only a Member of Congress can introduce a bill (or "measure") for consideration. The actual text of proposed bills frequently is drafted by legislative aides working either for members of Congress or for congressional committees. Occasionally you will encounter the same piece of legislation being introduced as a companion bill in both Chambers.
The President can propose a bill, and even send Congress a Presidential message urging its enactment into law, but he cannot introduce it. The President usually sends draft legislation to Congress with a letter or other explanatory material discussing his reasons for submitting the legislation. Sometimes the House will order a Presidential bill and its explanatory material to be printed as an official House Document.