@RH-Hutchins My advice for HTML, or anything, and NP++, or anything, is to aim small. If you type “aim small” into Google you will discover there’s a second part and it’s “aim small, miss small” but it all starts with “aim small.”
Work on understanding small pieces that are easy to chew and swallow. If you come across something that seems too large to consume comfortably then cut it into smaller pieces.
HTML in itself is a huge topic. Most of the web developers I have run across seem to know 1% or of HTML. When they need to work on a web page developed by someone else they often throw out the old/previous work as their 1% does not line up with the 1% of the previous developer.
As far as using NP++ goes, I myself use plain NP++ with no plugins or other special support for HTML. I test the HTML code using a web browser.