I sometimes still get involved with beginners to the web. Yes, nearly everyone knows how to Facebook, buy from eBay or Google for this and that but this is with the consumer hat on – fewer people have a basic knowledge of the atomic elements that make up a webpage. Here are some leads.
W3Schools has been there for a long time. It is still well presented reference and there are some areas where you can edit some HTML interactively and see the result.
Shay Howe’s Beginner’s Guide and Advanced Guide covers significant points.
Learn CSS Layout is a deconstructive tutorial.
jQuery from the source.
Adobe Dreamweaver reference and Help center
Scan your webpage and produce several screenshots with different browsers using BrowserStack