In the early days of the Web, almost all Web sites were what are known as 'static' sites. Site contents (text, images, video, audio, etc.), were placed or embedded in files, and these files used HTML (HyperText Markup Language) 'tags' to format those contents. Looking at actual files, might reveal something like this:
The content and the tags lived side-by-side. To edit the page, a file (on a local computer) would be opened in a program capable of editing HTML. Changes to either the content or the presentation would be completed, and the file would then overwrite the original stored on the remote Web server. Every page had to be edited individually, even if changes were for common elements that appeared on many pages (like menu bars, for example).
From a technical perspective, accessing a static Web site is fairly straightforward. When your computer is connected to the Internet, you can use a Web browser to access files on a Web server (as long as you know the address). The Web server delivers the contents of those files to your browser, and your browser displays them.
As the Web became more sophisticated, new systems emerged to more efficiently create and manage Web sites. Web applications – software that runs on a Web server making it possible to manage a Web site, came to provide sophisticated features. One feature of these Web applications allowed key changes (such as a navigation menu) to be made once and dynamically update all other instances across a Web site. Another improvement involved the separation of content from the presentation of a Web page. This allowed a Web site to change its look without requiring a complete revision of all written content it contained. To achieve this aim, many Web applications, like WordPress, were designed to store most content (text, images, etc.) and fundamental data about a Web site (its title, a list of authors) in a database, rather than in multiple places within numerous static files.
On the Web server, the Web application installs files that are written in some kind of programming language. The server reads this code and obeys any requests in it to access data in the associated database, and displays content according to instructions in the code.
Essentially, the data for the site (living in a series of tables in a database) is entirely separate from the actual presentation rules of a site (living in the code of the programmed files on the Web server). Special software enables everything to work together.
One of the benefits of using a Web application is that you usually don’t need to touch (or even look at!) the code in order to make changes to your content. In addition, editing a site usually involves accessing some kind of control panel through a Web browser and filling out a form, instead of having to download, revise, and upload files.
Generally speaking, it IS easier to regularly update content on a dynamic Web site because the Web application just makes it easier. It's especially easier to update the look of a Web site, because dynamic Web applications typically offer ways to do this quickly and without great effort (for example, WordPress employs "themes").