man is short for manual.
It's useful for many things, but only gives information. I'm not sure what you mean by codes, but it does tell you (if you're looking at the manpage of a command) the various options.
Generally you just type man followed by a command or possibly file you want the page for. You can also do man -k keyword and get a list of manpages matching the key word. Its best just to try it out tho
EDIT: just realised i should have given you a much simpler answer:
just run "man man"