Steem-bounty creates the comment. Everybody that upvotes the post on steem-bounty.com actually upvotes the comment. that comment is shared with the author of the post.

New comments are created when needed. this can max happen once per week.

From and end user perspective all you do is upvote the post. the UI hides the complexity. You can upvote once per week. The green upvote button after your upvote turns grey after each pay period.