Please note that FVM is catered for advanced users and developers.
If you are not sure about the options, I suggest leaving the default options on, or testing the other options on a staging/clone version of your live site.
There are a lot of options to solve conflicts and other issues, but for that one, I think it’s quite explanatory.
PLugins or your theme, may be loading font-awesome.
And if it does, it will probably be in the format of some file named font-awesome.css
Font-awesome files are generally big files, but are not critical to the styling of the page. Therefore, we can make them load async with lower priority to prevent the render blocking message on pagespeed insights, at the same time we reduce the size of the main CSS file.
So, if any of your plugins include a font awesome css file, where it’s url includes “font-awesome” (and only if), you have 3 ways of processing it.
a) default, will either inline or merge it together, depending on the other css options.
b) will load it on lower priority. Icons will show up later, after page load… but you need to see if it works. Multiple plugins may be enqueueing their own font-awesome files of different versions, so this may not work as intended.
c) same as b) but will exclude this file from loading to the pagespeed insights tool, since it’s not in the critical path.
In doubt, choose a) or leave the defaults.
Hiring a developer will also be good if you want to make full use of the plugin, as he will understand what this means.