Authentication throught LDAP: how?I'm getting crazy

Hello there, I have to make an authentication server using LDAP but, after setting up the server (openldap), I don't know what to do and where to go.

LDAP is a protocol for directory browsing so I don't know what has to do with authentication...it supports different authentication methods ok, but they are just for accessing to directories!

My project consists of a central server containing different kind of resources (documents, images, ecc.), user has to log in using an ldap server(???) and, if successful, can access.

How can I make ldap authentication and how can I make ldap server say to the other server "ehy mate, this guy is ok let him/her enter!" ?