You can create posts for social media directly in the app. Compose an image and add a caption and then tap the icon for your social media or messaging platform of choice. If you do not see you app or platform, tap the share button. You should see an option for sending the image to the platform there.
The keyboard extension works in most messaging apps but not for most social media posts. There are technical and security related reasons for this, but we expect that this will change in the coming months.
Currently you cannot add our stickers to Facebook comments. We are working on a solution for this and we will release it as soon as we can.