All the emoji art and services works in the main message apps like iMessage, whatsapp and in social media platforms like Facebook or instagram. How to use it will depend on the emoji service you choose.
Emoji Art & Emoji Sticker App (iMessage)
The emoji art will be just emoji illustrations on your phone gallery and you will send and post them like any other picture. It happens the same with the sticker option, but it will work on iMessage without leaving the app.
If you choose the full emoji keyboard, you can use that keyboard in all platforms, send them through the app or save them to your phone gallery.