In Drupal 8, you cannot anymore disable modules: You can just install or uninstall them. Uninstalling a module has the same effect it had on Drupal 7 and previous versions: It removes the database tables the module installed.
On /admin/modules, Drupal shows you which modules are not installed, and which modules are installed. You can click the checkbox shown for the modules that aren't installed; clicking on Install at the bottom of the page will install them.
For installed modules, clicking on the checkbox shown before the module name doesn't have any effect. In fact, the checkbox is disabled.
To uninstall a module from the user interface, you just go to /admin/modules/uninstall (or click on the Uninstall tab visible on /admin/modules).
Select the modules you want to uninstall, and click on the Uninstall button shown on the bottom of the page.
Keep in mind that Drupal can still not being able to uninstall a module for various reasons, for example because the module implements an entity and you created those entities on the site.
You could also use Drupal Console for uninstalling a module, but you would need to install it (on the server). After you install it, and open a terminal window on the Drupal root directory of the site, with
drupal module:uninstall <module_name> you would uninstall the
From the user interface it's easier. It's the only possible way, if you are working on a remote site for which the provider doesn't allow you to use an SSH shell.