To start the game, all you have to do is to open your friends chat and then type @FbChess Play to start playing the game.
Although, the game just being in its initial stages has many drawbacks because of which you might not want to even try playing the game.
Like most other dedicated chess games available on the Google Play Store or e Apple App Store which have touch implementation, Facebooks chess game works in a very different way.
Suppose you have to move a pawn, you will have to manually type "@FbChess e4" (without quotations) to move it to space e4. Do not worry, Facebook isn't expecting you to remember all the moves, if you want to know how and where to move a player, you just have to type "@FbChess Help" onto your message and you will be shown the further steps from there.
Of course, it is not as good as the other chess apps built, you surely can use this to pass your time with a friend. It works on all platforms including desktops.
So.. When is the game beginning!?