If you’ve been in the WordPress world for a while, the question in the title of this piece might seem absurdly basic. After all, plugins are a key part of the success of WordPress and every WordPress site uses at least a few. But for someone new to blogging, online publishing, or creating a site for their business, it may not be at all clear what plugins are and the part they play in a WordPress site.

Faced with a brand-new WordPress installation and no prior knowledge, plugins are the admin section most likely to confuse, and since WordPress is all about being inclusive, it’s useful to explain the basics.

Plugins Extend What WordPress Can Do

When WordPress is first installed, it’s a fully-functional but basic content management system. It includes everything you need to publish content online, but it doesn’t include everything you might want. That’s because everyone wants something different.

WordPress is used to build sites from small-scale blogs to massive publishing ventures, from single-page portfolios to enterprise-scale document management systems. If WordPress Core included everything that every user of WordPress might need, it would be enormous, slow, and extremely complex and expensive to develop.

Instead, the WordPress team focuses on building an excellent core experience while providing an interface that other developers can use to add features to WordPress.

Let’s take a look at the simplest possible example. When you first install WordPress and look in the Plugins section of the Admin menu, you’ll see a couple of plugins that are installed by default, one of which is called Hello Dolly. You might wonder what Hello Dolly does; the answer is that it does nothing useful — it prints out a random lyric from the song: “Hello Dolly”. It’s a harmless in-joke, but it does serve a useful purpose in that it demonstrates the basics of what a WordPress plugin is and how it works.

If you look at your site’s file system in your web hosting control panel, you’ll see a set of folders, one of which is called wp-content, within which is another folder called plugins. Hello Dolly and other WordPress plugins live in here. Each plugin is simply a set of PHP — the language WordPress is written in — files, along with associated assets like images. Most will also store data in the WordPress database.

Hello Dolly does nothing useful, but most plugins will add a feature or behavior to WordPress that is useful to at least some WordPress users. WordPress SEO, for example, adds features that help WordPress users optimize their content for search engines.

Where Do You Get WordPress Plugins?

The best place to find WordPress plugins is the WordPress plugin repository. There you’ll find thousands of excellent plugins to add almost any feature or behavior you might want to your site. Best of all, plugins in the WordPress plugin repository are free.

Not all plugins are free. Some developers create plugins that add features to WordPress that users are willing to pay for. Some offer paid support for their plugins. WordPress SEO — which I mentioned earlier — has a free version in the plugin repository and a premium version that users pay for.

A word of warning here. Plugins insert code into your site, which means that if there is any malicious code in a plugin, your site can be compromised. Online criminals like to put malicious code in pirate versions of premium plugins and make them available on-line. You should make sure you get premium and free plugins from reputable sources.

Hopefully, that’s cleared up any confusion you may have had about plugins. If you’re new to WordPress, I suggest that you take a look at the list of most popular plugins, you’ll almost certainly find at least one plugin on the list that adds a feature you want.