Code puts stuff in a box. Any tags/code you put there will be displayed instead of becoming interactive or just changing the text in some way.
Like this:
CODE
[code]Stuff
More stuff[/code]
This will be shown as:
CODE
Stuff
More stuff
List. Well, it puts stuff in a list
CODE
[list]Line 1
Line 2
Line 3
[/list]
This will show like this:
Line 1
Line 2
Line 3
Image.
CODE
[img]www.webpage.com/some_image.jpg[/img]
That will load the image between the [img] tags into your post.
Url.
CODE
[url]www.somewebpage.com[/url]
That will create an interactive link to the webpage.
CODE
[url=www.somewebpage.com]Link text[/url]
That will create an interactive link that will show as "Link text" and will take you to the www.somewebpage.com address.