There are a few ways to import stickers to Notability, but I recommend this process:
Download the files
Download straight to your device, or download on your computer, email/airdrop the files to yourself and open the email on your device and download to the Files app.
Unzip the Folder
In the Files app, unzip file folder by tapping on the compressed folder. Wait a few moments for the folder to be created containing the files.
You’ll find folders for Frames, Inspirational quotes, Headers, and more. Tap on one of these folders.
Split the View
To split the iPad screen you need to gently swipe up from the bottom of your screen until you see the dock appear.
The ‘iPad Dock‘ shows your favorite apps or those that you have opened recently.
Tap and hold the Notability app, then drag it to either side of the screen to start the split view.