This topic has been closed for further comments. You can use the search bar to find a similar topic, or create a new one by clicking Create Topic at the top of the page.
You make a queue containing the tracks you want in the playlist, then save the queue to a playlist. Saving the queue is available from the queue view. You can also add a track to a playlist by choosing the (. . . ) to the right of the track. Note, you cannot add tracks on a mobile device to a playlist, only from My Music Library or music services.