1. Always have a backup of your WordPress site, belt and braces is best. Use your file manager or FTP to make a copy of the site and use and export your WordPress database using mySQLi admin on your local PC.
2. Plugins can interact with each other so try out the plugin with the others inactivated first. Then re-activate one by one and check out the site.
3. Make sure you have the latest version of the plugin preferably via the WordPress site.
4. Check out the plugin is still valid with updates of WordPress, if not consider deactivating until it is.

Check out the tutorial on how to install WordPress plugins.