If you are a shared hosting customer, Plesk enables you to easily manage all aspects of your web hosting account using a web interface that is robust, but easy to learn. This includes creating domains, mail accounts, databases, and much more.
If you are a server administrator, or a web designer, it helps you to manage websites belonging to your organization or your customers, and also comes with a powerful suite of tools you can use to manage the server itself, as well as configure the many features and services of Plesk to your liking.