Is this whole system setup just to xomunally watch this one music video? Is there Seriously no button that I can. Press to ADD a video to the playlis???
The system you described would be very limited in its audience
I assume you’ve seen the help page by now, but if not, here it is: How to use Watch2gether?
TL;DR - Search for content (bar at the top), scroll down to see the results, and then add to the playlist by clicking the Plus icon below your selected video.