There are millions of different customizations available so your avatar can look like you do in real life, only in cartoon form. Once it's set up, you can use the Avatar version of yourself as a sticker in comments, stories, and messages on Facebook.
Here's how to set up Facebook Avatars:
That's all there is to it. Facebook automatically uploads your avatar into its system so you can post it anywhere you'd leave a comment. You can also send stickers in texts and other apps through the share button.