it uses some source of power (usually AC outlet but there are also solid state Tesla coils that operate from DC).
it converts that energy into high frequency AC (in original, spark gap was used, in solid state, electronic oscillator is used). in case of solid state version, this "AC" in primary is actually pulsed DC.
high ratio coreless transformer is used to produce high voltage.
Comments
That was the most simple and easy way with just a few parts to generate extremely high pulsing voltage source discovered by Tesla in those days.
it produces high voltage:
it uses some source of power (usually AC outlet but there are also solid state Tesla coils that operate from DC).
it converts that energy into high frequency AC (in original, spark gap was used, in solid state, electronic oscillator is used). in case of solid state version, this "AC" in primary is actually pulsed DC.
high ratio coreless transformer is used to produce high voltage.