Hi carmen,
check this document:
ADS-Userlocition is to find under point
2.1.3 Checking the User and Password
In case you do not know the user and password, you have to ask the basis-admins. They should have the right informations.
Normally you do not have to know about the ADS-User and password, because it is used like an webservice and it's configured central for the whole system.
Regards
Florian