what's the difference between a single and two stage air compressor?

i got this new unit from tsc on sale so why not make a video bout it? thanks for watching

https://www.youtube.com/watch?v=qCfJcNcJN_I

http://covenantnetworksupport.com/whats-the-difference-between-a-single-and-two-stage-air-compressor/