Go to the "Contests - Win Free Stuff" forum .... read the rules and post accordingly. At the end of the contest a number generator is used to pick the number corresponding to the post number in that contest, and they're the winner. Contests stipulate that you can only post once a day. At the end of the contest the winner will be notified by PM (for mailing address).
Currently the Road Runner contest & Driftmaster Rod Transport contest are active. Ketchn will post his contest in that same forum.