An LDAP server's database is organized hierarchically, typically with different branches in the tree for users, groups, and other services. This page allows you to select where in the LDAP database to search for different types of information, and how deep to search for each.
By default, all searches will be done under the Global search base. However, because most servers put users and groups under different sub-trees, you will probably need to set the Base for Unix users and Base for Unix groups to the distinguished names for those sub-trees. The Base for Unix passwords should be set to the same DN as Base for Unix users, as password information is almost always stored with other user attributes.