Take a look here 
"Until webside download links become available for forge maps in Halo: the Master Chief Collection, we strongly recommend use of the following framework for sharing your map. Play the mission "The Pillar of Autumn" in Halo CE on easy difficulty with competitive timing activated. This will allow you to appear on the game's leaderboards under that mission. From here, other members will be able to add you on Xbox Live and view your file share from the game's leaderboards. We recommend this particular mission with these settings in order to maintain consistency. We urge all forgers to complete this mission with these settings to streamline the file share viewing process for everyone."
Screenshots are a little difficult. I'd suggest that you create a film using the Xbox record app and then upload it to the interwebs, where you can take screenshots of the video using prt scr.
