new to offset printing

I have a few questions for the printing community. I am interested in learning about offset printing.
my first question is: how is an image turned into film negatives?
if i have an image that has green on one side and green and black on backside, do i need a 1 or 2 color offset press, how many plates would be required?

thank you all for your help. again I am just getting my hands into the printing world.

 

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