You need smallish goals and little projects that you actually care about. Start with javascript for some UI effect for your blog, for example. Starting with a whole PHP/MySQL site may be too much at once. And let's face it: the first few sites you create are going to barely work. I am a database expert but it took me a really long time before I understood SQL well enough to be comfortable with it, and a really long time after that before my skills could gel enough to really take off quickly. But along the way I had a continuous need to use databases.

After time your smallish projects get increasing ambitious. Javascript can't do something you need, move up to PHP. I "learned" languages by reading books or even taking classes but I have long since forgotten everything that I never actually had a need to use in the real world. I "learned" C but I remember things from javascript that I learned 12 years ago because I've actively used javascript on and off since then.

You need a CS degree to answer some programmer interview questions and as a quality indicator for kids right out of school, but plenty of really solid developers started learning by taking up smallish web dev tasks that became increasingly and increasingly ambitious over time. To get really good it takes years and years of doing this though.