There is not an 'official' way to run a contest, you just kinda make it up.
So, lets say you do a post/tutorial on something specific... like using a speedlight as a rim light. you then announce the 'contest' with the qualifications to enter; timespan (7 days typically to align to post payout), requirements for the image (must be a new image created for the contest, must use a speedlight as a rim light, whatever you want...), and then decide the payout. several other contests run something like 50% of the post payout to the winner, 12.5% to the next 2 runners-up (or honorable mention or the like). you get to keep the other 25% after the post pays out, you announce the winner and transfer the SBD :) make sure to tag the post with 'contest' and 'photography' as well as any other tag you would normally give it.
It might take a while for a new contest to take off, but it could be fun and profitable :)