vpopmail:- How can we efficiently use uid & gid

Hello friends.
I am using qmail with vpopmail. And I have also enabled mysql support for it.
I am setting permissions for domains & user accounts using vmoddomlimits & vmoduser.
when I set any value using these commands then one value get stored in pw_gid column of domainname_com table.
for eg. if I give command ./vmoduser -p user@domainname.com
Value of pw_gid becomes 2.
can anybody tell me that, is their exist any document which can tell me which digit in gid is used for what permission.
Like 2 is for disable pop access. So that I can display all the permissions in my GUI.
In short I want to ask why gid is used & how can we use it effeciently.
Or is their an other way to access these permissions.
Also tell me what is uid & how we can use it.
Also it will be nice if some can tell me what is the purpose of dir_control table & how I can use it.

Thanks in advance
Amit

I tried various search terms on google. But I am unable to find anything.
I tried following terms

1. gid values vpopmail
2. vmoddomlimits vmoduser
3. vpopmail mysql guide
4. pw_gid
5. pw_gid values
6. pw_gid vs pw_flags

Can anbody pls help ???

I also tried

qmailrocks.org
vqadmin
lifewithqmail.com

But I am unable to get anything out of that as well.
Can any body pls help ???

Amit

I don't know what is the problem is here.
This is a very big forum.
But why no one is replying to my problem ??
Am I not clear in my Question ?
or is it too difficult ??
or it is just not possible to do it like that ???
What exactly the problem is ??????????????