It uses your upvote, when you not, and when you make a post you will get upvoted by the other member with the same amount you have given....at the moument it give you around 5 times your own upvote value.
There is a more detailed post about it here ;-)
https://steemit.com/steemit/@upvotebank/gzsr5aw6
actually, they do
Downvoting a post can decrease pending rewards and make it less visible. Common reasons:
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