I am very confused. I have never written code that looks like that. It is the -> and the printf (which has never made sense to me) that have me stumped.

$foo->bar() is a method call on an object, and Foo->bar() is a method call on a class. See perlboot and perltoot for tutorials.

printf is one of Date::Manip::Delta's methods, so you can find its documentation there. Or if it's the whole idea of printf() and its friends and relations that confuses you even after reading the sprintf manpage on your system, then I suggest reading chapters 1 and 7 of Kernighan and Ritchie's "The C Programming Language".