Understanding the Codex?

Hey everybody,

I’m pretty boggled by this WordPress system, but I’ll try to ask a question the best I know how.

I’ve been told to read the codex, but…I don’t understand really what it is. Is it set-up by WordPress or developers? I’m going through themes and having a real tough time figuring out what is pre-defined functionality and what is arbitrary to each devleoper’s deifition.

My main objective right now is to just get a basic image in a header.php file.

I found this:

http://codex.wordpress.org/Function_Reference/bloginfo

From what I gather it looks like a list of examples for defiinng and referring to variables. However, how do I use bloginfo(‘variableName’); to refer to an image?

Do I at least have the right idea even using bloginfo()?

If anybody could let me know if I’m hot or cold, I’d really appreciate it.