#File Foo.pm
sub make_foo
{
   # do stuff
}

#File Bar.pm
package Bar;
use Foo;

sub make_bar
{
   &make_foo(); # It is defined here.
   # do stuff
}

#File myScript.pl
#!/usr/local/bin/perl -w
use strict;
use Bar;
use Foo;

&make_foo(); # Undefined subroutine!