You place your bet via Twitter, therefore you need a Twitter Account. Just click on one of the 'Place bet' Links and post the tweet with the provided text. You may change the text, but the tags and link have to be untouched! After sending the tweet, it will be recognized shortly after.
Re-Tweets of your post will count, too!
Only one vote per match counts, if you tweet the text more often, only the last tweet will count.