https://www.cnet.com/news/whatsapp-to-add-stickers-encourages-artists-to-create-more/

To use them, you just tap the new sticker button and make your choice.

The company is trying to inspire other artists to make more by releasing a set of APIs and interfaces that allow you to create new third-party sticker packs that can be added to the initial set via the Google Play Store or Apple's App Store.