PHP is a server scripting language, and a powerful tool for making dynamic and interactive Web pages. PHP is a widely-used, free, and efficient. With PHP, you can add large database to you website or app. It is a very advanced language with all built-in features. Also it is easier to learn than other progamming languages.
This tutorial is from W3C which is "THE WORLD'S LARGEST WEB DEVELOPER SITE". This tutorial will teach you PHP from basic to advanced level including forms, database, XML, AJAX etc. They also have online editor for PHP.
This video tutorial is from Bucky Roberts Website. It has 200 videos. It will take you from a beginner to somewhat advanced level. You will learn to code many projects like Registration form, Validation, SQL Injection, Protecting Email etc. A highly recommended video series for beginners learning PHP.