Here are the URLs that contain very useful information about LDAP. >From these URLs, this HOWTO was made, so if after reading this document you need more specific information, you probably will find here:
University of Michigan LDAP Page: http://www.umich.edu/~dirsvcs/ldap/
University of Michigan LDAP Documentation Page: http://www.umich.edu/~dirsvcs/ldap/doc/
OpenLDAP Administrator's Guide (brother document): http://www.openldap.org/doc/admin
Linux Directory Service: http://www.rage.net/ldap/
Red Hat and LDAP: http://www.redhat.com/docs/manuals/linux/RHL-9-Manual/ref-guide/ch-ldap.html
Mandrake Linux - Using OpenLDAP for Authentication: http://www.mandrakesecure.net/en/docs/ldap-auth.php
Integrating OpenLDAP with other Open Source projects: ftp://kalamazoolinux.org/pub/pdf/ldapv3.pdf