Sentry client for Joomla! is a plugin that helps you tracking errors on your website. The extension is a very simple interface for the great Sentry application. You can get more informations about how to use Sentry on the official website. If you want you can also go on the project Github repository and read the doc to learn how to run it on your own server.
To get started, simply create an account on Sentry official web site, follow the steps until your project is fully configured. Once you get the DSN, simply paste it in the plugin configuration and you are done !