A plugin is a piece of code that adds functionality to your WordPress site. Using plugins and widgets you can customize your blog in all sorts of ways without writing a single piece of code.
Free plugins that have been approved by WordPress can be downloaded from the WordPress Plugin Directory.
You can see which plugins are installed on your site by vising the Plugins menu in your WordPress control panel. From here you can also add new ones, and browse or search the Plugin Directory for more.
Not all plugins are created equal, however, because not all programmers are created equal, and not all plugins have been updated to meet current coding and security standards. When looking at a plugin in the Directory, pay attention to the ratings, the number of downloads, how recently it was updated, and whether it’s been tested with the latest version of WordPress. Also take a look at the support tab, and see how responsive the plugin author is to questions and problems.
And although plugins can be fun, remember that each one has the possibility of slowing your site down. Try to keep your plugins under control, but if they are well-written, and your hosting company is reasonably fast, you should be able to handle up to 15 plugins without any issues.