To make validating a pages HTML easy, create a new bookmark in your browser (for any page at this point), name it something like ‘HTML Checker’, then edit the URL for the bookmark to just contain this JavaScript code:
javascript:void(document.location='http://validator.w3.org/check?charset=%28detect+automatically%29&doctype=Inline&ss=1&group=0&verbose=1&uri='+escape(document.location))
When you next visit a webpage, and click your new bookmark, it will automatically take that websites URL address and run the validation check and output your results on the w3 website. Try it yourself!