Replace the default images in the Assets folder with logos more relevant to your app. Make sure you adjust your images to the necessary dimensions of the logos 30×30 (SmallLogo), 150×150 (Logo), 310×150 (wideLogo), etc.
If you want your app to start in a particular orientation, or use a specific capability (webcam, internet, location, etc.), be sure to specify this in Package.appxmanifest, which contains metadata for your app and is everything that Windows 8 needs to know about your app.
You’re off to a great start! Be sure to check out more app development resources from Microsoft Developer & Platform Evangelism to help you bring that great app idea to life.