Before you can use the LDAP calls you will need to know...
The name or address of the directory server you will use
The "base dn" of the server (the part of the world directory that is held on this server, which could be "o=My Company,c=US")
Whether you need a password to access the server (many servers will provide read access for an "anonymous bind" but require a password for anything else)
The typical sequence of LDAP calls you will make in an application will follow this pattern:
ldap_connect() // establish connection to server | ldap_bind() // anonymous or authenticated "login" | do something like search or update the directory and display the results | ldap_close() // "logout"