How do I post images using BBCode?

Okay, I've read the help sections, I know the basics but I'm useless with this kind of thing so can someone please spell it out for me?

I know I need to use the code: [img [/img]

But what goes between them exactly??

I usually use photobucket as my image hosting site, but which one do I use for the BBCode? The IM, the Direct Link, HTML code or the IMG code?

I've tried a few different combos and they don't seem to work

It's to have images appear in my signature on a forum

Thank you!