Websites which have a Database Backend, tend to have a few scripts, which pull information from a database, and create a page on-the-fly.
The Script takes the information from the database and presents it in a uniform manner. This means each page has the same format and style, keeping a consistent look across your website.
Because the information and the script are separate, it makes it very easy to create another page, just by adding more information to the database.
Also it is easy to add or remove things. An example would be a list of companies which pay a subscription to have adverts listed. When a subscription expires, (or is re-newed,) a simple on-off style adjustment can be made, to remove (or re-add) them.
Almost all Websites built with a Content Management System use a database to store the information in a website. The CMS merely changes this data to update the website itself.