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It is quite easy. All you have to do, is buy a share and then you get your upvotes for 29 days. 1 share is 4 STEEM (that you have to send to their account) and buys you 150 delegated Steem Power for that time.
You can read more about it from their intro post

https://steemit.com/steemit/@minnowpowerup/introducing-minnowpowerup-learn-how-to-power-up-the-smart-way