HTML code in posts

Are you allowed to use HTML coding in posts?

I know of the alternative [ b ] [ / b ] types and so on for simple text emphasis, but what about the others?

< Font > tags? for size, colour?

marquees?

It would be nice to post a screenshot instead of an image, as well.
< center >
< img= >
< /center >

you get the picture (pun intended)