You can think of it like this.. Twine is the "foundation" for the html page, and then Sugarcube, Harlowe, etc are all the language formats for it.
Depending on what you are wanting to create - Sugarcube has much more potential for greater complexity if needed, while both are pretty easy to just build a simple "page > link > page" game. Sugarcube is better supported and documented I think.
You must be registered to see the links
- < authors site (aka TheMadExile on some other forums)
HiEv who is around on F95 here is also pretty high up the chain on coding for Twine in general (just by my viewer opinion) as I have seen HiEv consult on various projects when help or suggestions were needed.