Every game on dot big bang can be played and edited in multiplayer mode. First, you need to make sure your game is Saved and Published. Click the icon in the top right corner, name your game, and click Save.
Once your game is saved, your can invite other people to join you in it. Click the share icon to open a multiplayer session of this game, and then press the Copy button. Send the link address to your friend, and press the Go! button yourself to switch to a version of your game that anyone with the link can join.