There’s no HTML around.
Choicescript does have a rather steep learning curve if you’re not used to coding at all. I know when I started I was completely lost with it and it took a while for it to click into place. It’s worth it though since once you learn how to use it it’s a lot more versatile than those gamebooks. It’s also code designed for those without any coding knowledge.
I’d say take your gamebook on TextAdventures and try and translate it into choicescript. If you need help on how to just ask and we’ll help. (Or perhaps you can point us at it.)
I’ve found that by far the best way to learn to write games in choicescript is to start by reading their code.
https://www.choiceofgames.com/dragon/scenes/startup.txt is Choice of the Dragon and since it’s a simple game I’ve found it good to start.
Once you’ve got a bit of a start I’ve a short tutorial I wrote to try and help people out with some of the basics. A Basic Tutorial on Name, Relationship and Gender Variables
Also it’s of vital importance that you use a text editor (like notepad or notepad++) and not a word processor (like word) in order to write your choicescript games.