This is not a script, this is a LDAP filter which means :
(&(objectCategory=person)(objectClass=user)(givenName=*)(sn=*))
Retrieve the entries which are of the type person AND user AND
which possess these attributes populated : givenName AND sn
If you want to retrieve the groups which these users are member of, configure on the tool that you want to also retrieve the attribute memberOf from the users entries filtered.
As stated in the Subject of the question, if you want to know the members of the group MyGroupName, retrieve the member attribute of this group filtered by a LDAP filter, for example, such as :
(&(objectClass=groupOfUniqueNames)(cn=MyGroupName))