i mean how i can think about that

It was all thought previously, and Fletch already gave you a link to follow.

Get a copy of webmin and see how that software does the task you describe; all the details are there.

The procedures to add or delete users from the system differ greatly with the underlying OS and the specific configuration of the host on which to perform these tasks. As Fletch wrote, there are different schemes: passwd and shadow files, LDAP, NIS, NIS+, PAM, differing system utilities that take care of user's home directories, skeleton files used to set up acounts and so on.

If you want to write your own CGI to handle all that, go ahead, but look at webmin as a reference and starting point. Be aware that any process which modifies security tokens must run under UID 0, i.e. as root, which generally isn't the case with apache, so you need suexec...

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}