On other SA hubs, direct drive was the middle gear. You can change the sprocket to raise/lower the overall gearing to suit your terrain. Or the chainring, of course.

You unscrewed the shift chain coming out of the hub from a cable connector in order to remove the rear wheel. Takes a few seconds. The connector also has a barrel adjuster to set shift tension.

You could use an indexed downtube shifter to shift if you wanted. Or an old SunTour ratcheting shifter. Or a thumb shifter.