This is just a quick summary. I guess a separate presentation video explaining the numbers only belongs on the todo list.
Personally I think the concept is easy to understand (we count tweets and followers and bet on stuff) and the there's a /help/game page to explain the very details.
Tweets = number of tweets (retweets and urls are ignored) - if you post 100 tweets, this number grows by 100
Tweeters = number of unique accounts that posted tweets - if you post 100 tweets, this number grows by 1
Total Followers = number of followers the tweeters had - if you post a tweet (or more tweets) and you have 12 followers, this number grows by 12
Maximum Followers = the biggest number of followers observed on a Twitter account
Average Followers = total followers divided by number of tweeters