Reference code. Start at the top and work down.
The four languages, one at a time. No databases, no servers talking to each other — just the building blocks.
HTML CSS & Bootstrap JavaScript PHPMaking pages talk to each other and to a database. This is where a website starts becoming a web app.
Forms Databases Sessions RedirectingUpdating a page without reloading it, logging users in, drawing, and the odd useful trick.
Ajax Modals Login systems Canvas ExtrasTip: many of these pages print their own source code instead of running, so you can read exactly how they work. If a page looks like it "did nothing", view its source in the browser too.