Go to the session of congress you want to know about. Click the Senator in the box, check "sponsored", then search. It will bring up all legislation sponsored by the Senator.
John Kerry sponsored 48 pieces of legislation in the last congress the last time I checked.
Do this for each session of Congress Kerry was there for. You can change search criteria to restrict it to bills passed or bills that became law or ones voted on.
Keep in mind that minority party Senators have a difficult time getting legislation passed since the majority controls the calender. GOP has controlled the Senate for 14 of the 20 years that Kerry was Senator.
108th Congress (2003-2004)