App Customizer Settings
The settings tab allows you to add information about your app such as title, author, and more.
Choose a menu for your app. The App Menu selection will appear as a side menu, the tabs menu will be tabs. You can select one or the other, or both.
To create a new menu, go to Menus => Add New. Add items to your menu and save. You may have to refresh the page to see this menu on the settings tab.
Enable Push Notifications
Check this box and rebuild to enable push notifications in your app.
This will have no effect if you have not already setup your push profiles correctly under Apps => My App => Push Notifications.
Enter your app details, such as title, author, website, etc.
Icon and Splash Screens
Upload the appropriately sized images here, and they will be converted into all the necessary sizes for different devices such as phones and tablets.
Universal splash screen - upload one 2732px by 2732px .png image. This image will be cropped, so make sure any logos or critical text is small in the center. Download a sample image here.
These must be .png files at the exact specified dimensions or it will not work properly. Optimizing your .png files using a service like TinyPNG or WebsitePlanet's compressor to a small file size is recommended.
Please see this article.