If you're creating a WordPress site, to add functionality to your site, you need to add plugins. This is so because if you interfere with the core WordPress files, all your functionalities may get overwritten by core WordPress files again on updating. Therefore, to add any functionality to your WordPress file, you need to add a plugin using approved WordPress APIs.
These plugins can be simple as well as complicated; this entirely depends on what you want to do. The simplest plugin is a PHP file. Thus, we may say that plugins allow you to add functionality to your website without even touching core WordPress files.
If you have a WordPress website and wish to add functionality to it without even developing plugins, you may contact us. We offer to develop plugins for WordPress sites at an affordable rate. All you need to do is- get in touch with our trained and experienced professionals and explain the functionalities that you wish to add.