I want to add permanently boxes below Visual/HTML editor for each page/post. I’ve never played with custom fields before, and I’m not sure is it way to go?
If yes ten tell me, good people of StackExchange, how to achieve something like that (grey boxes):
Your looking for custom meta fields, which you can style anyway you want using CSS.
http://codex.wordpress.org/Custom_Fields
You would either have to write your own functions to accomplish this or use one of the many custom fields plugins, I would recommend the WPAlchemy MetaBox.