Hi there. I presume you have read the Moodle documentation on LDAP authentication http://docs.moodle.org/22/en/LDAP_authentication ? Are you in an establishment that uses LDAP? Are you in charge of that as well or is there perhaps a network manager who could assist? In the meantime remember that you don't need LDAP for your students still to be able to register and work in Moodle - (we have active directory but just have ours signing in twice) Hopefully someone will be able to advise you soon
EDIT I just saw your other post re your server - are you sure you need LDAP? What about simple email-based self registration? Check it out here http://docs.moodle.org/22/en/Email-based_self-registration