I can't find good documentation on what all the "*,(.*)", "s")" does
You won't find any Roku-specific documentation regarding the syntax of regular expressions, as they are not a Roku-specific feature. Regular expressions are implemented in many languages on many platforms. The different implementations have much in common, so any resource on learning regular expressions in general can be helpful, as long as you are aware that Roku implements Perl-compatible regular expressions (PCRE).
They are, however, an advanced programming feature, albeit an extremely useful one, and as such the learning curve can be quite steep.
If you really want to learn regular expressions, you could:
read the documentation: https://www.amazon.com/Mastering-Regular-Expressions-Jeffrey-Friedl/dp/0596528124
take on online course: https://www.google.com/#q=how+to+learn+regular+expressions