What's the difference between generating a value and returning a value?

[grocery_stocker]

Taken from the url....

http://openbookproject.net/thinkCSpy/ch05.xhtml#index15

"The built-in functions we have used, such as abs,
pow, and max, have produced results.  Calling each of
these functions generates a value, which we usually assign to a
variable or
use as part of an expression.


biggest = max(3, 7, 2, 5)
x = abs(3 - 11) + 10

But so far, none of the functions we have written has returned a
value.

In this chapter, we are going to write functions that return values,
which
we will call fruitful functions,"

So what's the difference between generating a value and returning a
value?