For both the hierarchy structures, you need to define roles and assign it to users. A user can be associated to only one role at a time.
Role Hierarchy - In this structure, access to a user's data is based on the roles. Users at higher hierarchy can view the data of users in the subordinate roles. For instance, Zylker Inc. follows the below hierarchy structure, here the CEO or Administrator can view the entire organization's data. And, the Sales Managers can view the data of all the Sales Executives. See Also Manage Roles.
Reporting Hierarchy - In this structure, unlike role hierarchy, a user can be assigned a reporting manager who can view the data. Any member at the higher role in the organization can be assigned as the user's reporting manager. See Also Reporting Hierarchy.