Yes = Buy
No = Short
This is a permanent market and its duration will be lengthened as long as it's allowed. The aim is to sell your stock (see top right after you've made a bet) when you believe your side has over-corrected and buy in/short it again once it's over-corrected to the other side. Essentially, it's meant to function like a traditional stock market.
Read more: https://help.manifold.markets/manifold-101/why-would-you-sell-your-shares