Create

In game hit Y to bring up your menu then hit RB for "menu and online features". Highlight and select "Community Challenges" on the upper left. Pick which challenge you would like to submit an entry to, doesn't matter which and then hit A to submit. This will bring up your online gallery and you can submit anything you have...doesn't necessarily have to relate to the challenge, the achievement still pops. If you do not have anything in your online gallery to submit all you have to do is after you complete a challenge, hit X to take a "Snapshot" and upload it online. Hope this helps :)