Drupal scans specific folder locations to identify modules and themes defined by the .info.yml file in their directory. The following is the order in which projects will be discovered:

By placing the module inside the root modules folder, we are allowing Drupal to discover the module and allow it to be installed. When a module is installed, Drupal will register its code with the system through the module_installer service. The service will check for required dependencies and prompt them to be enabled if required. The configuration system will run any configuration definitions provided by the module on installation. If there are conflicting configuration items, the module will not be installed.

A theme is installed through the theme_installer service and sets any default configuration by the theme along with rebuilding the theme registry. Setting a theme to default is a configuration change in system.theme.default to the theme's machine name (in the recipe, it would be bootstrap).

Although it is not the required way to install an extension, this should become your default method. Why? Because each module is a dependency in your project, and each of those may have its own dependencies. Composer can manage dependencies for you, or you can manage them manually. Your time and capabilities probably will not grow to scale as well as Composer will. Not to mention, it also provides a standard way for PHP projects to interoperate and load classes.

You can get the Honeypot module and Bootstrap using the following two commands:

$ cd /path/to/drupal8
$ composer require drupal/honeypot$ composer require drupal/bootstrap

Here is an example of contributed projects, which require Composer for installation, because they leverage existing libraries in the PHP community at large:

As more and more modules integrate existing SDK libraries, the requirement to use Composer will increase.

Modules can be downloaded and enabled through the command line using drush. The command to replicate the recipe would resemble the following:

$ drush pm-download honeypot$ drush pm-enable honeypot

It will prompt you to confirm your action. If there were dependencies for the module, it would ask whether you will like to enable those, too.

One of the substantial changes in Drupal 8 is the module disable and uninstall process. Previously, modules were first disabled and then uninstalled once disabled. This created a confusing process, which would disable its features, but not clean up any database schema changes. In Drupal 8, modules cannot just be disabled but must be uninstalled. This ensures that when a module is uninstalled it can safely be removed from the code base.

A module can only be uninstalled if it is not a dependency of another module or does not have a configuration item in use--such as a field type--which could disrupt the installation's integrity.