How is returning the output of a function different from printing it?

Question

In my previous question, Andrew Jaffe writes:

In addition to all of the other hints and tips, I think you\'re missing something crucial: your functio

Answer 1

def add(x, y):
    return x+y

That way it can then become a variable.

sum = add(3, 5)

print(sum)

But if the 'add' function print the output 'sum' would then be None as action would have already taken place after it being assigned.