Ok, so far and till this point, you could have tested everything as an HTML5 application. For the development process, this works, but with mobile devices you should also start testing on a device very early. They have much less computing power than a desktop PC. And if you run into a performance problem, well you can only detect this on the device.
Anyway, when you build and transfer your app onto a device, it will always have the name Monkey Game, by default, and a default icon. For sure, you want to change that.
Google has a pretty good description of how icons have to be designed for certain usage. At the time of writing this book, the information is available at: http://developer.android.com/guide/practices/ui_guidelines/icon_design.html.
There, under Providing Density-Specific Icon Sets, is described which sizes they should have. Basically, you need three icons, 36 x 36, 48 x 48, and 72 x 72 pixels, in dimension. So, create these three icons as...