If you download digital stickers from the GoodNotes shop, they will directly be added to the Elements tool and are ready to use. If you download them from elsewhere, you can import them:
You can draw anything in GoodNotes and save it directly as a stickers with the Elements Tool.
Elements can be anything created with GoodNotes tools, namely handwriting, shapes, images, text boxes, and any combination of those. All elements are organised into 'Collections', in much the same way as Folders in the app organise your notes and notebooks. This helps ensure that your elements are easy to find and categorised for quick access.
Besides online stores like Etsy, you can easily find more digital stickers in GoodNotes directly. Tap the shopping bag icon in the top right corner in Library view to go to the in-app shop! New stickers are added every month.