The gallery can feed items either from manually input – by clicking the blue plus sign and adding items.
Either from YouTube user channel. You just need the channel username in the YouTube User field to make it work.
Either from a YouTube playlist. All you have to do to find the ID is access your YouTube account and go to the Playlists section. Create a new playlist or select one of your already created ones. The link should look like this – http://www.youtube.com/playlist?list=PLADC18FE37410D250&feature=plcp – the id is ADC18FE37410D250 – never include the PL part too if it’s there at the beggining.
Either from a Vimeo user channel. If you go to a user profile for example – https://vimeo.com/user9682578 – the is the number after the user part in this case – 9682578