Perl operators and functions can be used to manipulate data and perform other necessary tasks
The difference between operators and functions is blurred; most can behave in either way
Chapter 3 of your Camel book, perldoc perlop, perldoc perlfunc, and perldoc -f functionname can be used to find out detailed information about operators and functions.
Functions can accept arguments of various kinds
Functions may return scalars, lists etc
Return values may differ depending on whether a function is called in scalar or list context