mailbox prefix

dovecot version 2.2.13

hello, I try to make a new server just for me after having old one working for ages with Dovecot, Fetchmail, Squirrelmail, Procmail making new one with above plus Postfix using Maildir structure. I am having a bit of trouble understanding exactly what the namespace and prefix are. Is the "private/" prefix an internal thing with Dovecot ? Or is it supposed to be a real directory ? I'm not quite sure how to properly address the INBOX in Procmail, Squirrelmail, Postfix config.

for example am I supposed to say inbox is ".private/.INBOX"

cheers

zemlik