SparkySKO wrote:

[Basically this says, are there any practical alternatives to an air
variable capacitor that a beginner can use in building his first
receiver radio?]

This homebrew 10-600pF book-shaped air variable has knob tuning:
http://www.leradiodisophie.it/CV-libro.html

Wind a simple coil, add a diode and audio amplification -
see what you can hear.