If you have a video that you want to add to a playlist:
-underneath the video on the left side, there is an option that says "add to" with a + sign next to it
-click on the + sign
-an empty long box should pop up
-under that the option "create new playlist" should pop up
-click on that and type the name of the playlist you want to create
-click on the blue box underneath that says "create"
-when you want to add more videos to that playlist, click on the "add to" and will bring up a list of the playlists you have created
I hope that made sense. The only way I can give these instructions is to go to you tube and actually create a playlist so I can explain it
You can make as many playlists as you like. If you have multiple playlists, you can just click on "add to" and move down to select the one you want to use.