What I understand about Steem-Bounty is that you allocate an amount of STEEM which will then be distributed to all the people whose comments you've upvoted for. You have to send the STEEM amount to the Steem-Bounty account (@steem-bounty) and in the memo, you put your post link. At the end of the 7 days, they will distribute that amount among the ones you upvoted.

That's the way I've done it.