This documentation section is yet to be updated and it is about proper ways to extend Zero One theme and make something super powerful.
There are some good general rules you should consider doing:
Make some kind of documentation of your template files changes. Primarily because you can take advantage of our theme updates, and not overwrite your changes.
When you want to change page templates the best approach would be to copy existing template and by changing it create new template. The same goes for snippets.