W3Schools is the mother of all internet tutorial sites — and unlike most things from that era, it is still going strong.
Free tutorials covering:
- HTML, CSS and JavaScript (including modern layout with Flexbox and Grid, and up-to-date JavaScript)
- Server-side topics: SQL, PHP, Node.js, Python and ASP.NET
- XML and related technologies (XSLT, XPath, XQuery, XML DOM, WSDL, Schema)
- Web building basics: W3C standards, browsers, accessibility, hosting and certification
The killer feature is still the “Try it Yourself” editor: every example runs live in the browser, so you can tweak the code and see the result immediately. If you need something for your CV, they also run an online certification program.
Start at w3schools.com.