How to use regex capturing groups?

[anijatsu]

I can't figure how to use this plugin, with the single readme page of documentation not describing the available toggles or the CSS styling sufficiently well. Like - what do the "capture group" toggle actually do? Are there dynamic classes created per each capture group? etc.
My regex rule is as follows:
/([0-9\/]+)\s([0-9:\.]+){1}\s+([\w\-]+){1} (?:\s+says)?((\s: )?.+)/gm
And a sample text line I'd like to apply it to is as follows:
11/30 00:05:15.233 Person looks to their right.
I want to use group 3 and group 4, giving each of them a separate style, e.g.:
11/30 00:05:15.233 Person looks to their right.