I am designing a map game, using PHP and MYSQL. I don't know how to make the players who sign-in to the website to see other players who are also connected to the site and be able to chat with one another.

I want to design the game in such a way that 2 players can play with each other and be able to send messages during the game while others groups are playing at the same time.

I have designed the map game successfully, but the problem is making the player 1 who log-in to site to see the player 2 who will also log-in and both can get connected to play each other. http://i.stack.imgur.com/YyCPG.png

I will appreciate your responses.