I guess I should start with the obvious: What is PHP?
PHP is a scripting language that helps to create dynamic web pages- similar to JavaScript in this respect. However unlike JavaScript, PHP is a server-side language (as opposed to client-side). This means that the server carries out the instructions given to it by PHP, and then returns an output in the form of HTML.
With all this talk of JS, don’t think they’re the same thing. PHP is a general-purpose scripting language and is considerably more powerful than JavaScript. PHP is the bread and butter of web-based scripting- it’s used to create 99% of the websites you visit on a daily basis, making it the most popular scripting language on the net.
PHP may be powerful, but its also extremely flexible and easy to use. With PHP you could create an entire website from the ground up (and indeed many people do), or just scatter the odd line here and there. Either way, once you know what PHP can do, you’ll never look back.