If enabled, this option will give you the possibility to cite your video sources.
Select any video from the library and navigate to the Credits / Source field in the video details section.
All you need to do is input the source of that specific video as a text entry.
Save the changes and once the video is embedded, you will see something like this:
For videos imported from YouTube, you can either manually add the source, or enable the option to automatically fill source/credits. In this case, all your videos fetched from YouTube will automatically display the name of the channel as the source.
Automatic fill is enabled on the site level. Once you have a site selected, click on the cogwheel button right next to the site's name and navigate to the options section.
Please note: Disabling this option will only affect newly added videos. Previously uploaded videos will still display the credits/source text. Once re-enabled, the change is applicable to all YouTube videos imported from that point on.