Summarize this article in one sentence.
This will open your options on a drop-down menu. Alternatively, you can click the three-dot icon next to a song or album. It will open the same menu. A list of all your playlists will pop up. This will add the selected song or album to your collaborative playlist. Other users will be able to view, play, or remove these songs on the collaborative playlist.

Summary:
Right-click on the song or album you want to add. Hover over Add to Playlist on the menu. Select your collaborative playlist on the list.