can you tell me how the bar code reader works?

can you tell me how the bar code reader works?
how the bar code is formed and how the bar code reader works. do we need to install a bar code reader software in order to get the bar code read. how the prices are derived from those lines.

Best answer:

check this site
taltech.com/TALtech_web/resources/intro_to_bc/bcpwork.htm