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So you simply press on the song title and it starts playing. I.e each track is represented by a horizontal bar about 1cm high, with the three stacked dots symbol to the right edge. Just press anywhere in the bar (except the dots) and the track plays.
Once you've done that and the track is running, you see the track playing bar slide up from the bottom of the screen. You can press on that to open the track as full screen, winth artwork and other function keys (pause, skip, etc).