How it works:

If user logs in to Joomla CMS then LDAP plugin checks if such user exists on LDAP server and if YES then he successfully authorize user.

LDAP plugin doesn't work as synchronization utility, as it adds new non-existed users into Joomla only, but doesn't synchronize user profiles between Joomla and LDAP server in the future. I.e. if user information will be changed in LDAP then we'll get 2 different users.

PHP with LDAP support.

Ask the LDAP server administrator for the settings:
  - ldap server name;
  - ldap server port (usually 3268 or 389);
  - ldap dc;
  - domain name;