This is the code browsers receive that they then use to build (known as rendering) a website page.
You'll usually find a mass of code here which is impossible to understand unless you have some technical knowledge but it is possible to search out particular elements.
I'm Tim Hill, a Search Engine Optimization and Online Marketing specialist. I created this site to help others understand that SEO is not a mysterious black art!.
If your a newbie try the Getting Started in SEO page, otherwise feel free to dig around and learn more.