Hi Leo,
The documentation regarding the development of the websites can be found here, it's covering all the aspects for both MVC 5 and MVC Core approaches. Where things are Core-only relevant, you can find these here, for example this is an article of integrating Xperience with Core Identity (login). Also, the link you provided, covers both Core and MVC 5, it works in Core as well. And this is an example of adding a user to a role.
In most scenarios searching through the docs and API examples should bring you relevant answers. But if you are having more specific question - don't hesitate to ask here at DevNet QnA or on the Slack channel.