I think the only one people will be really interested in is what tessspoon posted, but, to elaborate, you can put anything you want inside the [url][/url] tag.
For instance, you can put a suffer icon inside it like so:
[url=http://www.google.com/]:suffer:[/url]
and it will become this:

That might not be so useful, but, if you have caught on by now, you can put images within [url][/url] tags as well.
The great thing about a forum like this is that you don't have to physically type in
everything yourself if your browser supports JavaScript and has it enabled.
So instead of typing out:
[url=http://www.google.com/]:suffer:[/url]
All you have to do is:
- Click the suffer icon.
Your text will now include :suffer: in it. - Highlight the :suffer: text.
- Click the
icon. - Edit the [url] to point to your web address.
For instance: [url=http://www.google.com/]
You can go
here for a full explanation of all the BBC tags on this forum.
Now, to discuss HTML and CSS.
Technically, BB code is not HTML or CSS. Rather, BB code was a markup language created for security purposes as well as giving more formatting control to the programmer and less formatting control to the users. Also, I can reason why it would be easier to program the use of BBC tags rather than programming certain HTML tags to be allowed.
There are most certainly parallels between BB code and HTML though.
For example, [b][/b] in BBC is equivalent to <b></b> in HTML.
Therefore, if you understand exactly how to use BB code, it is a very short step from there to learning simple HTML.
CSS is very different from both BBC and HTML; however, it has a lot to do with HTML and absolutely nothing to do with BBC.
CSS was created to go along with HTML to make it easier to style uniformly across multiple browsers. It also was created to solve a growing problem of messy HTML code. Styling HTML through HTML tags alone made the code extremely bulky as well as messy and difficult to maintain. Also, developers were using certain HTML tags for styling purposes when their original intent was not meant for styling. Doing this can and will lead to several improper displays of web pages on certain devices or browsers.
I feel it's slightly too complicated to explain how one uses CSS in a thread such as this. If you want to learn more about HTML or CSS, a good resource is
http://www.w3schools.com/. For really simple explanations, I have heard
this website explains things easily. It's built for kids anyway.