I also don't understand what you mean. You should add the domain in the advanced settings of DirectAdmin.
exactly. I would like to redirect domain or subdomain to directory under public_html
as I see, I can only add domain to directadmin, then a new folder appears a level above. but what if I want to redirect .com domain (or subdomain created in directadmin) to a subfolder?
I am still not really sure what you want to achive and why, but if you want a doamin to have its root in /public_html/blaha/ instead of /domains/domain.com/public_html/ I guess you could use a symbolic link pointing at the desired root directory.
Maybe mod_rewrite also could be used to achive something similar.