XHTML is a stricter version of HTML.. You have to code tidier in XHTML .. I can try to answer as many questions you have but I have little monkeys doing most of the HTML work that I do nowadays

Btw this site strips most of the HTML when you post here

I once found this site that "teaches" the very basics of HTML:

http://htmliseasy.com/index.html

You may find it useful.

you should add something else... most of the time when its a paragraph its.. replace the brackets with the arrows..

( p style="font-size: 21px;" ) and then end it with (/p)

everything in html should be wrapped... p or span  or div etc

It doesn't work on this site

? no you can have everything in pixels..
pixels is measurement in html.. there are others like percentage %, pica's, em's but pixels and percentage are the most used

width ="200px" or height="200px"

..like how i made the quoted table smaller 

(a href="www.link.com") its a link to go another web page (/a)

And a list of all colors? Lol... You won't learn then all there are 16 million within RGB.. http://html-color-codes.info/
But there are more colors for HTML then just the #000000 RGB ones

Are you using an IDE?

Glypicons aren't always available.. Just like fontawesome.. A site can choose to support these or not.. Glypicons are supported in bootstrap.. A popular framework with tools to build a HTML site

I don't know them out of the head.. But a glyphicon or fontawesome should display an icon.. Like a car, arrow, star.. Not a lot of sites support them..

your own avatar clickable is impossible.. cause you can't access that part of the site.. but it can be done in the sig..

I replaced < with (

(a href="http://www.linktowhereyouwanttogo.com")(img src="http://www.imagelink.com")(/a)

basicly you will be wrapping the img tag with an a tag

- edit 3 minutes later- 

ah... vgchartz text editor seems to strip it away....