W3Schools, I'm sorry to say, has some horribly outdated tutorials. Please don't start there.
The best way to learn PHP is to start with something like a simple to-do list app. There are many tutorials that can help you get an idea of how to go about it. It'll make you comfortable with some of the conventions of PHP, how mysql queries work, some of the very basics (loops, variables, using arrays, etc.)
Install XAMPP on your computer and start with your first one-page app. At the same time, sign up to Stackoverflow and ask questions over there. You will learn a lot. The most important thing is to learn how to think a program — 90% of the code is in your head. PHP isn't a particularly difficult language to understand. In fact, it's newbie friendly and it won't take you a lot of time to learn.
Best of luck!