Trial version of RH2022

To add to Peter's explanation, in RH2017 you choose whether you're creating a character style, paragraph style, list style etc This equates to the p, h1, a, ol, etc tags you can pick in RH2022. The Class is equivalent to the style name you give the style in RH2017.

The pseudo class says to apply styling to the tag/class only in specific pre-defined circumstances. You pick the circumstance in this field. The most common use historically is for links, to set a different colour for visited links, or change the colour or underline when you hover the mouse over a link, for example. In HTML5/CSS3 more pseudo classes available and they apply to more tags than just the "a" tag.

The W3Schools link Peter provided is part of a larger tutorial all about CSS. It looks daunting but the pages are actually quite easy to understand and there are "Try it" links so you can have a play to better understand the functionality. I recommend referencing it whenever you find something CSS related you don't understand. Then use the MDN link for more detailed information and technical explanations once you're comfortable with the basics (or if what you're looking for isn't covered by the W3Schools site.

Google gives me this. Pseudo-classes - CSS: Cascading Style Sheets | MDN (mozilla.org)

Also try CSS Pseudo-classes (w3schools.com)

A class is something like p.red where you have set font to have red text or some other characteristics.

These can all be set up in the CSS editor.

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My site www.grainge.org includes many free Authoring and RoboHelp resources that may be of help.

I'd use Peter's site as a guide - grainge.org