Foo and bar are just demonstration variables. They are used just in examples, when the thing being demonstrated is not the actual implementation of the code, but just a concept.

Shift removes the first item from the @_ array (or another array if one is provided to the function, or @ARGV if not used in a subroutine) and puts it in $whatever. So if you had this:
my @foo = ('bar', 'quux'); my $whatever = shift @foo;
$whatever would contain 'bar,' and @foo would contain only the 'quux' element.

edit: thanks thelenm - fixed

Quinn Slack
perl -e 's ssfhjok qupyrqs&&tr sfjkohpyuqrspitnrapj"hs&&eval&&s&&&'