Modification of Drupal Required Modules
Required Modules preinstalled with Drupal have to be enabled for Drupal to run. You can’t disable or delete them but some of the required modules allow the administrator to modify specific settings.
Drupal's Block module
You can use the Block module settings to control in which regions Drupal displays various content. It’s worth taking another look at the Block module interface. There are two ways to access the Block module interface:
From the Dashboard menu bar, you can choose Structure→Blocks.
From the Dashboard menu bar, you choose Modules. Then you scroll down until you find the Blocks column and click Configure.
If you access Blocks via the Modules overlay, click the Help link in the Block column. This displays some useful rules that may come in handy when you’re working with blocks.
Drupal's Filter module
The Filter module is responsible for three types of content filtering:
Filtered HTML: This filter removes HTML code when you choose to restrict certain HTML tags. The filter also attempts to find and correct faulty code. For example, if the HTML is missing a close-table tag, </table>, this filter adds it. The HTML corrector applies only when HTML code is allowed. You can also restrict all HTML tags and this filter will remove them.
Full HTML: This filter converts carriage returns and line feeds into HTML tags.
Any time you create text content, Drupal scans it and looks for carriage returns or line breaks. When you type text into a text box to create a story or posting, the Filter module converts your carriage returns and line breaks into HTML style line breaks. Without this, your carriage returns won't show up in the browser when you publish your story.
This all happens behind the scenes, so you can type away without worrying about the HTML side of things.
URL Filter: When you’re creating content and you type a URL (for example, www.drupalfordummies.com), after you publish it, Drupal turns it into a clickable link. This also applies to mailto links (for example, <mailto://firstname.lastname@example.org>).
Drupal's Node module
Because nodes contain every bit of the content on your site, the Node module controls how content is created and submitted. You use the administration links for the Node module to manage content types, edit and delete submitted content, and manage how posts to the front page behave.
The only settings you can change for the Node module itself are how the roles can interact with content. These settings are found on the Permissions page at Administer→User Management→Permissions.
Drupal's System module
The System module contains the code that runs Drupal. To get an idea of all the areas under the umbrella of this module, choose Modules@@→System, and locate the column on the page titled System.
The System module controls, among other things, these:
Site Information: Settings for the entire site, such as site name, e-mail address for automated e-mails to users.
Actions: Tasks that Drupal can do automatically when something happens.
Cron: Allows Drupal to do routine site maintenance automatically.
Drupal's User module
The User module controls everything to do with roles, user accounts, and access rules and permissions.
You may have noticed that many of the modules listed on the Modules overlay have a Permissions link. The Permissions link controls who can change the settings associated with the associated module. In general, unless you trust your authenticated users or article editors implicitly, you should never give anyone permission to control anything under the Core modules.