Once you've completed your ad, simply press the preview button located on the bottom right hand corner of your Playground build.
The preview should launch to a new window with your ad in an iPhone frame. The URL of this page is now shareable to other users and mobile devices for testing.
Tips for testing your Ad Creative
Chrome Dev Tools
Your Chrome browser has inbuilt tools to help test and identify errors in your mobile creative.
Review Google's Chrome Dev Tools guide for tips on launching dev tools, inspecting elements, using the console etc.
If you've made changes to the basic template it's important for you to test your changes on device. PLAYGROUND ads support iOS 8/9 and Android Kit Kat and up. You should ideally test on a range of devices. If you don't have access to physical devices you can use virtual devices on Browser Stack.
Sharing your URL to mobile
The easiest way to share your Share URL to your mobile device is through scanning QR codes. Chrome has an easy to use extension that will generate a barcode of your Share URL. You can download a QR code reader on the Google Play or Apple App Store to read your generated code.