PHP (or “Personal Home Page”) is the most popular scripting language for the web. Nowadays, it is used as an alternative to Microsoft’s ASP (“Active Server Pages'') technology. It is free, open source, and server-side (which means that the code is executed on the server), used to make dynamic web pages.
MySQL is a Relational Database Management System, or RDBMS (which is software that is used to store, manage, query, and retrieve data in a relational database), that uses what’s called Structured Query Language (SQL). SQL is also open source, and is the most popular language for compiling, retrieving, and managing data in a database. It is known for its accessibility, speed, reliability, flexibility, and ease of use.
Just about every open source PHP application uses MySQL to function, and the PHP language provides functions that make communicating with MySQL extremely simple. The PHP functions are used to send SQL queries to the database. Since the PHP handles the details, you’ll only need to know the SQL queries and how to use the PHP functions.