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Hi @lienminh,
Please read our info post: https://steemit.com/steemit/@upvotebank/gzsr5aw6
In short the service will use your vote, when you don´t and when it uses your vote, your vote value is added to your account. The next post you make will be upvoted by the other member with the amount saved up. (for now the max is 5 times you own vote value, in your case 0.05$)
Hope it make sense :-/