To vote for MapleUnity, you have to make sure you are logged in on the website. You do not have to log out of the game to vote.
Then, simply press the vote button and you will be brought to the GTOP website. Here, you have to fill in the captcha to prove that you are not a robot.
And then press the big red button to send your vote through.
Your account receive your Unity Cash automatically within a couple of minutes.