Where can I find more information about macros and structures?
I read thefasm manual but think the documentation is incomplete.
Maybe I'm just to used to learn from examples...

Try this link
http://decard.net/?body=tajga&chapter=preproc

thanks silkodyssey for the link, just what I needed.
Feel a bit stupid, spent a time exploring the site and found quit a bit on macros.
However your link deals with preprocessor directives and macros in from the ground up.