My streaming source is almost exclusively from my NAS, with an occasional stream from Amazon music or Tunein.
Streaming from my NAS, I start something playing, usually an album, then I tap the browse "<" in the top left hand corner until I navigate back to albums or artists. In an album folder, you can tap the three dots, and one of the options is Add to Queue, or you can add single tracks to the right of the track listing by tapping the 3 dots there, and selecting the add to queue option. That's also where the Add to playlist option is.