Processing is better for creating content for webpages rather than the webpages themselves. The areas to look at are HTML5 and Processing JS

http://www.w3schools.com/ is a good starting point

Personally, I never liked this site (w3schools), I found the information they gave to be partial, and sometime even incorrect.
I was amused when I saw I was no alone in thinking that: http://w3fools.com/
That said, there are plenty of other good sites to learn HTML.