You need to understand the purpose of each CI class and each attribute that needs to be populated in the CMDB. Discuss with appropriate stakeholders whenever you are not clear or need more details. Then you can check either from the dictionary or from the CI class manager ('Attributes' tab of each class) to see the attributes available OOB. Some of these attributes would be common or easy to understand. For the attributes which you don't understand and also if you can't find a matching attribute for any of your requirements, check online or raise a hi-ticket to confirm the availability of suitable OOB attributes. Create custom attributes only when you confirm that an attribute is important and not available OOB.
