Screenshots are taken from the live iOS app, however the app is exactly the same on Android.
Please view these guides on desktop, as these pages are not optimised for mobile (yet).
1. After purchase, go to the Home Screen and then tap on your Individual Items policy.
2. Tap on the item you want to add documents for, and tap the "Add photo" button.
3. Take a photo or choose one from your library, and it will be added to your item details.