For 14, you're doing better than a lot of "seasoned" developers except for one major thing...
Your layout is busted here. Your sidebar is UNDERNEATH the content column.
You are declaring width:100% on pretty much everything, and that's just not going to fly; particularly when the default behavior of a DIV is to expand to the available space. Likewise a max-width on an outermost container would really help as right now your content paragraphs are expanding to the point where they are hard to read.
There are some minor other issues -- like you are using the same ID more than once; ID's are unique and should only be on a page ONCE, you want more than once that's a class' job.
You are declaring your font sizes in pixels -- that is an accessibility issue that prevents text from dynamically scaling to user preferences. It's a "tough read" but the WCAG says to use dynamic (em) fonts for a reason; the only time to resort to PX is when there's a image interaction like with Gilder-levin image replacement
There are multiple separate stylesheets for no reason other than slowing down the site and making it harder to maintain -- the more separate files you have, the more handshakes and the slower your first-load. Likewise you have no MEDIA attribute on your CSS link. Given what you have for style I'd suggest making that media="screen,projection,tv" since you styles probably don't make a whole lot of sense for things like PRINT or AURAL.
Some logical document structure probably wouldn't hurt either -- horizontal rules between or headings for each of those little subsections of text would provide structure that using DIV simply does not provide, since DIV have no semantic meaning other than "This element MAY receive an unspecified style". Even if you hide the HR, their structural meaning would help search engines and screen readers not treat the entire page as a single article. Allegedly HTML 5's pointless "SECTION" tag does the same job... I'm not sold on that since HTML 5 seems to just encourage code bloat and take a giant leak on the structural rules.
Likewise the STYLE tag is invalid inside BODY, it MUST go in HEAD, and you seem to have a copy of your favicon code before the doctype, so IE is in 'quirks' mode.... and really you should avoid the STYLE attribute like it had leprosy... seriously. Likewise you have the CENTER tag in there, which has no business in a HTML 5 doctype much less on ANY website written after 1997. Seriously, it was deprecated (meaning "don't use it") sixteen years ago. We've been told not to use it longer than you've been alive... that people still do so is... that's it's still in many tutorials is... yeah.
I'd also suggest you not use names like "leftcontainer" and "rightcontainer" -- say what things ARE, not what they look like. This will pay off when you get into more advanced concepts like responsive layout, where what's a single column may end up broken into multiple, and what's multiple columns may end up combined into one.
Still for all that, at 14 you're doing better than a LOT of people out there charging money for this stuff. Give you a year or two with some proper instruction and learning, and you'll be kicking names and taking ... wait, that's not right.