Some tips from Drupal Administrator's Guide
General terms
Module
A module is a piece of code which extends Drupal to provide a specific piece of functionality. Some modules are part of the core Drupal system (eg. the taxonomy and blog modules) and some others (eg. the weblinks and image modules). Core modules are those included with the main download of Drupal. Contributed (or "contrib") modules are available for separate download from the modules section of downloads. Be sure that the version of the contrib module you wish to use matches your version of Drupal. The releases section lists modules by Drupal version.
Node
Nodes are probably the hardest Drupal concept to grasp but they are really quite simple. Almost all content in Drupal is stored as a node. When people refer to "a node" all they mean is a piece of content within Drupal, it could be a poll, a story, a book page an image etc.
Permissions
Permissions control access to content creation, modification and site administration. Administrators assign permissions to roles, then assign roles to users.
Roles
Roles are groups with certain permissions that can be applied to individual users. Users can belong to more than one role. Two roles, authenticated user (those users that sign up for an account) and anonymous users (those either without an account or not logged in) are the default roles of Drupal installations, but they can be configured and the first user can create additional roles.
Blog
Blogs, or weblogs, are another term for an online journal or diary. They are a place where members of the community can write their own thoughts and not have to worry about being ontopic for the site.
Best practices guidelines : Accounts and roles