No, the "URL" is the internet address - at the top of your screen you can see a toolbar where it says something like "http://uk.answers.yahoo.com"
That's the URL of the page you are on right now.
http://www.webopedia.com/TERM/U/URL.html
HTML is "hyper text mark-up language" - all you really need to know is that it's used for making clickable messages and links like this one:
http://en.wikipedia.org/wiki/HTML
Don't worry, you'll get used to it! Use the preview option before you post a photo on a website to check that it works. Sometimes you need the IMG code and sometimes the HTML.