For your information only few of them are supported by Emoji Kitchen.
okay so lets start
Lets open FB to post something
open G board's emoji. (Make sure G board is your default keyboard)
Select the emoji you like and make sure to test a few of them to see the one that is supported by Google
If the selected emoji can be modified or mix each other, Gboard will pop up few suggestions and it will take some time.
Select the one you like and it will be pushed to your post.
Please note this is just a beta version and an official one will be coming soon.