The Community Files (User Content) section is used to add your own videos, film clips and montages. Its being used more and more and this is just a simple guide on how to add content and additional content. Adding Content
NOTE: i screencapped this, and therefore you can see 'Add for user' which is a feature for Mods only.
VIDEOSFOR HALO REACHTo add a bungie rendered reach video, you need a specific url, example:
http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=1077353&player=edgified
this needs to be changed to:
http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=1077353&
FOR HALO 3
use this ID number in the ID box.
FOR YOUTUBE VIDEOShere is an example url - http://www.youtube.com/watch?v=XoXDzYd9364&feature=hp_SLN
inbetween the = and the & sign is the video ID -------- XoXDzYd9364&
again this ID can be copied into the file ID box.
IMAGESthe file ID for images, is the image url.
the image url can be found here:

click copy image url, and paste this into the file ID box.
right clicking on the image and copying the image url works for everything, bungie screenshots, photobucket, etc.
Additional Content
this box can be used to add the other parts to a video or extra screenshots along with the original content added, or you can add text, e.g. like a description for a image or video.

here is an example of other screenshots being added into the additional content, used to show the map.
Tip For Adding MapsWhen adding a map, you can choose to show a preview image.

This can be done using a bungie.net screenshot of the map, visit
http://www.bungie.net/, search your gamertag and find your screenshot.
Then you can save the screenshot onto your computer.

Once you have, you can upload it to photobucket, or any other place to share pictures. Photobucket link:
http://photobucket.com/Example:

Then right click on the image, and click 'Copy Image Url', as shown above.
Once copied you can past this into the 'Preview Image' box, as shown below.

Hope this guide helps.