phpMyAdmin is a feature-rich tool developed in PHP, which shall provide you with full control over a MySQL database. You can do literally everything - create fields, rows and tables, remove them or modify their content, export or import a whole database or only a particular part of it, and execute MySQL commands. The tool is necessary if you want to switch web hosting providers, simply because you could very easily generate a full backup of a database in several formats (SQL, CSV, XML). You shall end up with only one file containing the whole content of the database, so you could download it from the present provider, upload it to the hosting server of the new one and import it using the same tool on their end. Your website shall look exactly the same, simply because all script applications store their content in a database. With phpMyAdmin you may also conveniently search and replace content of your preference across the entire internet site - a word, an expression or a link, for instance.