Hi there,
If you are starting with Twine, I don't recommend using a template, but learning the basics of Twine first.
Twine is a program with multiple formats (Harlowe - default, SugarCube, and Chapbook), each having its own way of coding (formatting of the code, name of macros, symbols to use). I would recommend you check ou the Twine references to see how Twine (the program) works (create a new project, import a Twine project, selecting/changing a format, etc...).
Then, you may want to check out basics tutorials for making links between passages and tracking choices. I recommend Dan Cox's YouTube series (see listed on this page). If you are set on using SugarCube, I have a whole basics section in my guide, with code examples in action.
Twine also has a community where you can ask questions (find links to the Discord/Reddit/Forum here) and get an answer quicker.
If you are still set on using one of the templates here, the easiest method is to download the HTML version of the template, import it into Twine, make a duplicate, and start editing that duplicate!
If you still have an issue with a template, please tell me which template you are using (since each are different).
EDIT: please note that these templates are meant to be used in SugarCube in the latest version of Twine. I only have so far one Harlowe equivalent (here).