Perl (and really all code languages) are made up of various 'sets' of functions. You can bring in one of these sets with the 'use Text::ParseWords;' line, which enables you to use one of the functions in that set: 'quotewords'. I.e. if you remove that 'use' line from your file, the quotewords line will give you an error.

Code modularization and reuse are definitely important aspects of coding. I would say you should start to look into these topics in earnest once you have gotten comfortable writing a few 'basic hello world' examples from scratch on your own. In short: most advanced functionality you are looking for will be package in some module somewhere nowadays :). Hope that helps!