WordPress Plugins allow you to easily modify, customize, and enhance a WordPress site. Instead of changing the core program code of WordPress, you can add functionality with WordPress Plugins.
A WordPress Plugin is a program or a set of one or more functions written in the PHP scripting language, that adds a specific set of features or services to the WordPress site. You can seamlessly integrate a plugin with the site using access points and methods provided by the WordPress Plugin Application Program Interface (API).
Creating a plugin of your own is really not that difficult and can solve a lot of problems. Copying and pasting useful code and additional features into your theme’s functions.php file is great, but these changes may be lost when you update your theme. A plugin is a safe way to try out new things
This guide help you getting started with plugin development. A little knowledge of editing files and some rudimentary HTML and PHP is required for plugin development