What is a Plugin?
By making your own plugin you are extending WordPress, i.e. building additional functionality on top of what WordPress already offers. For example, you could write a plugin that displays links to the ten most recent posts on your site.
Or, using WordPress’ custom post types, you could write a plugin that creates a full-featured support ticketing system with email notifications, custom ticket statuses, and a client-facing portal. The possibilities are endless!
Most WordPress plugins are composed of many files, but a plugin really only needs one main file with a specifically formatted DocBlock in the header.
Hello Dolly, one of the first plugins, is only 100 lines long. Hello Dolly shows lyrics from the famous song in the WordPress admin. Some CSS is used in the PHP file to control how the lyric is styled.
As a WordPress.org plugin author, you have an amazing opportunity to create a plugin that will be installed, tinkered with, and loved by millions of WordPress users. All you need to do is turn your great idea into code. The Plugin Handbook is here to help you with that.