phpMyAdmin is a feature-rich tool coded in PHP, that will give you total control of a MySQL database. You could do virtually everything - set up fields, rows and tables, erase them or alter their content, export or import a whole database or just a certain part of it, and execute MySQL commands. The tool is necessary if you want to switch web hosting companies, due to the fact that you could very easily create a full backup of a database in different formats (SQL, CSV, XML). You'll end up with only one file containing the whole content of the database, so you could download it from the current provider, upload it to the web server of the new one and import it via the same tool on their end. Your site will look exactly the same, due to the fact that all script applications store their data inside a database. With phpMyAdmin you could also conveniently search and replace information of your preference across the entire website - a word, an expression or a link, for instance.
