I hope this screenshot helps.
When you upvote a post, after 7 days in our UI, we create a comment and use your upvote on that comment. We share the reward with the original author of the post and display in our UI how much the post has received via forever upvotes in green and original upvotes.
over time a post can generate more and more rewards this way.
Does this make more sense now?
RE: We are launching a new service called Steem-Forever