beginner question

[maumar at cost.it (Maurizio Marini)]

When configuring sw that should authenticate ldap, they ask for ldap admin and 
password
I wonder which is the difference between:
uid=admin,ou=Administrators,ou=TopologyManagement,o=NetscapeRoot
and 
cn=Directory Manager.
When shoud i use it ot the the other? who is "ldap admin"?
tia
	-m