How to get the related entities of an entity like account or contact in CRM

Hi,

I am new to CRM. I need to get all entities related to an entity like account or contact. For an account entity the related entities should be Appointments, Campaigns, Cases, Contacts etc.  I am not supposed to add any relationship, just need to retrieve the entities related to account or contact. I tried with below code but in the response object RetrieveAllEntitiesResponse -> results[0]. _relatedentities.  I have a property relatedentities  but the count is 0. Am I missing anything? or do I need add any code to get the related entities?

RetrieveAllEntitiesRequest retrieveAllEntitiesRequest = new RetrieveAllEntitiesRequest()
   {
    EntityFilters = EntityFilters.Entity | EntityFilters.Privileges | EntityFilters.Relationships,
    RetrieveAsIfPublished = false
   };