I have the same question, and I will follow you.
each yes share has an opposite no share. It's a zero sum game, as the yes +no =$1. You can't short sell, so when a contract launches, the only option is to buy. If you want to buy a yes at .20, then the option to buy a no at .80 appears, and vice versa. If someone takes you up on your offer, you get a share and they get a share.