Carl0c0s :   Well, for number 2, you have to at least be a regular member. Newbies can't use them. Since you are one, you are good to go. Now go to the edit profile and settings option in the top left corner of Vizzed, then you will see that edit layout has been moved. Click on the link, and you can there find the store to buy the layouts. Once you do that, go to my layouts, and select the one you want. Hope this helps. I don't know enough about the HTML thing, so somebody else has answer that.

HTML stands for "HyperText Markup Language".
It's the scripting language used to make web pages, every single webpage you see uses HTML in any way, shape or form (including Facebook, Google, Twitter etc.), usually in conjunction with CSS and/or php.
Even if the website is mostly flash (which some sadly are), it has to use HTML to embed that flash.
Depending on your browser, you can hit Ctrl+U to see any page's source code, you can even try it right on this page.

Layouts are also made of HTML too, so knowledge of it is required to make more advanced layouts, you can find tons of tutorials on it just by Googling it, but unless you actually are interested in the field, I don't think it's necessary for you to learn it.
A commonly used tutorial is the one by W3Schools, but it has its fair share of errors, so I'd recommend you to either use one of the actually good tutorials listed at W3Fools.com or at least read through W3Fools beforehand.