subdomain...

[expream]

Hello all! So i have a little problem, maybe can some one help me?:)


So... I habe my domain - my_domain.com - There is my site. But i have made subdomain - register_subdomain.my_domain.com. So user go to "register_subdomain.my_domain.com" and the he beginn registration. How can I do it? and he register name.my_domain.com