If you use a database-driven script app for your site, all of the content that you or the site users add, is saved in cells and tables in a database, not as ordinary text in the application files. In comparison, HTML websites are static and all of the content on such a site is a part of the actual HTML files. An online store app, for instance, takes all of the items, prices, user reviews, etc, from its database and this is valid for any other script which allows you to create a dynamic website. The more the info you insert, the larger the database will get, so when you use a script-driven site, you should make sure that your hosting package comes with enough database storage space. The aforementioned applies regardless of what kind of databases you will use - for instance MySQL or PostgreSQL.