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 30x30 (SmallLogo), 150x150 (Logo), 310x150 (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.