According to them
"Magpie is an ad network for Twitter.Our customers sign up and create campaigns which consist of magpie-tweets (i.e. ads). Twitterers allow us to post magpie-tweets among their tweets and get paid for it."
They provide a tool to check how much you can make with this network.I was surprised when i check my personal account with it .It says i can make 22euro per month with that services.Then think about the professional twitter users,and company how much they can make.
At fist you need to signup with your twitter password.And setup your tweets/ad-ratio.