what is means " document.querySelector("#scenario2Input #shuffle")."

Question

http://code.msdn.microsoft.com/windowsapps/ListView-custom-data-4dcfb128/view/Discussions

WinJS.Namespace.define("Scenario2Name", {
        initialize: function () {
            WinJS.UI.processAll();

            document.querySelector("#scenario2Input #shuffle").addEventListener("click", shuffleTiles, false);
            document.querySelector("#scenario2Input #removeSelected").addEventListener("click", removeSelected, false);
            document.querySelector("#scenario2Input #swapSelected").addEventListener("click", swapSelected, false);
            document.querySelector("#scenario2Input #addTile").addEventListener("click", addTile, false);

            initTiles();
        }
    });

document.querySelector("#scenario2Input #shuffle").

#scenario2Input --> where is from ?

# --> when to use it? what means?