Content needs to be managed and that's where Content Management Systems play a major role.  The Content Management System takes a complex task of managing a web site both for web site navigation and adding images / hyperlinks to a web page.  It's important to understand the organizational structure of a basic web site is based on a collection of individual pages that are 'linked' together to form a web site.  The idea of the 'web'  is based on the threads (or links) created by a spider.  Indeed search engine 'bots' are also called spiders because they follow all the threads (or links) and create a special kind of 'map' that helps it understand the relationship of pages and links. Managing a web site requires some kind of methodology to updating the content and then promoting the content. On a simple site this is  possible although challenging with changing content. On a medium to large site this becomes a daunting task.

Content management systems provide a container, much like a babushka doll that provides logical navigation and a built in hierarchy for nesting content. management of users, content, links, optional features all are components of content management.  All of this is powered by a database and some kind of scripting language like .ASP or .PHP   so the pages are built on demand from a database and then presented within the framework of a template.  This allows for thousands of pages to be created and managed  all within a GUI environment.  That is you are working in a familiar desktop environment  with icons and a graphical interface.

It's easy to confuse a content management system with a web log, or blog for short. A content management system can provide an excellent tool for blogging but it can also operate in the static hierarchy of a web site.  Blogs operate historically.  Current articles are listed at the top of the heap with older articles 'archived'. Variations on this include a traditional web site with a blog section which can be broken down by categories for a well defined content structure or a blog as the main site with some static pages following a more traditional layout.

It's important to remember that a CMS helps organize your site but you really need to plan out exactly your navigational structure before you begin.  Will you use a Section>>Category>>Article navigation layout which gives you the most exposure to keyword phrases or a quick and snappy Section>>article? Plan, plan and plan.  It does not get any plainer then that.