Alan : in the playing screen (not fullscreen) you have a button on the lower right. This button is a contextual "Options" button, that brings all other commands related to that item in focus (in this case the video you are playing) so if you click there you will find:

- save this video
- bookmark this video

Then after this you are able to go to your bookmarks on the youtube plugin main menu and see your videos that were bookmarked and play them from there.

BR

Marcelo