Where to find and how to use iMessage Stickers?
1. Open the Messages app.
2. Create a new message and add a recipient
3. Tap the App Store icon above the keyboard (“A” icon)
4. Tap the button with the four ellipse in the lower left corner.
5. Tap on the Store button (blue plus symbol)
6. Choose Manage tab (on the upper part of the screen)
7. Turn on the sticker you just activated before with the switch next to it.
8. Tap on Done, and now you can see the downloaded/activated Sticker Packs.
9. Choose the one you wanted!