A web designer needs to validate the HTML code inside a page. If you are paying a webmaster then doubly important: Use: W3C HTML Validation Service.
To have a page load properly, fast, efficiently, the manager of a web site needs to at least spot check essential pages.
I have an HTML page on my computer, this is my default page when I open a tab or window, or if I clicked home in my browser.
I make a link that looks like this:
I have it open in a new tab or window
Example: W3C HTML Validation of Code