In game screenshots

So could I get the messenger app on xbox to share screenshots on that?

You can upload screenshots on your xbox to onedrive, which you can access on a computer, you can do this by.

Going to the Upload app on your Xbox One and
choose the screenshot you want to share from Manage Captures. Press the Menu button and choose Share. The screenshot can
be uploaded to Twitter, OneDrive, your Xbox activity feed, private message, or your own personal showcase.
Choose the service you want to upload it to

You can share your screenshots to other services, like Twitter and OneDrive. The latter is good because you have access to it for free through your Microsoft account. From there, you can save it to your PC, edit it and post it elsewhere. Hope this helps!

Check if the game you are playing allows screenshots, as in some games it is not possible to take screenshots.

It depends on the game and what the Publishers want shown on the Store...some games have plenty of in-game gameplay