I was wondering do you require 5 different audio sources to create a 5.1 surround sound mix? does 5 channels = 5 sources?

I have 4 complete sources of a show, does this mean I can create a 4 channel mix? or will it be a 5 channel mix since all 4 will be combined to make the new 5th channel?

Maybe any links to tutorials or help/advice from pros