Hello, I am so lost here please help!

set = [‘a’, ‘b’, ‘c’]

binary_number = “101”

#produces the subset [‘a’, ‘c’]

#‘b’ is left out because its binary digit is 0

I don’t understand what the block of code above is written for in the lesson and how that binary_number variable produces subset ‘a’ and ‘c’ out of the blue.

Please save me from this mystery :((((((