These stickers are hand-drawn by a deaf woman for those who wish to communicate in ASL. They are animated GIFs and drawn sign language art.
The stickers allow you to communicate in full signs and concepts. For example: Good morning, Whats Up, Pah, Yes, No, Stop, How You, Awesome. These are just a few of the many signs.
If you are unsure how sticker apps work please go to this website https://support.apple.com/en-us/HT206906