How do I disable the default user system or view pages without login?
It depends on the type of page really, what module provides it, how permissions are implemented by that module - the short answer is by setting correct permissions at /admin/people/permissions. 

You can't disable the user module, it's a required part of Drupal. Conceptually, if you were to disable it you'd have no authentication control over the admin section, and any user could make whatever changes they wanted - obviously that's not a situation that can be allowed to exist for 99.99% of users. And if you do want that, you just need to set up permissions to allow it.

But you can stop users from registering, which avoids that problem. And by setting appropriate permissions you can decide exactly what users (or even groups of users, using the Roles system) can see/do.