BlockzUniverse (called Blockz by other people sometimes) is a multiplayer online game.
You control yourself with the arrow keys or WASD, and you jump with the spacebar. You can also zoom in and out with Z and S. You can interact with the left click, and get a menu for the block your cursor is on by the right click. You can chat by pressing "/" (slash).
You can use "/" (slash) to chat. There is also chat messages that are already there, in a menu. The list of things available in the chat menu are here: BlockzUniverse/Chat Menu