Plugins add functionality to your website, but they can also wreak havoc. You need to ensure that the plugin you are using has been updated to work with the most recent version of WordPress (and that you are using the most recent version). It is also important to remember that plugins offer added features and therefore can sometimes conflict with your other plugins aers nd themes. Remember to backup your site frequently when installing plugins. You should also test your site after installing each plugin to make sure it is operating properly before you add more plugins.
The WordPress Codex offers a detailed explanation of how to install and use plugins here.
