For the sake of your (search engine) Quality Score, (human) Credibility and (financial) bottom line, there are exactly six pages your site must include.
W3C Markup Validation Service, a free service that checks Web documents in formats like HTML and XHTML for conformance to W3C Recommendations and other standards.
“For people who make websites” A List Apart Magazine explores the design, development, and meaning of web content, with a special focus on techniques and benefits of designing with web standards.
MIT-licensed HTML5 template and CSS framework built for responsive design based on a 12-column grid. The boilerplate contains no JavaScript, just HTML, CSS and example site icons (favicon & iOS).
Full Web Building Tutorials - All Free
At W3Schools you will find all the Web-building tutorials you need, from basic HTML and XHTML to advanced XML, SQL, Database, Multimedia and WAP