To mass delete the data associated to a Users go to Setup | Administration Setup | Data Management | Mass Delete Record, select the objects e.g. Account and in criteria select the users name and delete all records of that user related to particular object.
Types of relationship fields in Salesfroce
2. Master Details
3. Hierarchical (User Obejct – Cannot be created)
4. Many to Many (Junction Object)
5. External Lookup (Lookup to Ext Object)
6. Indrect Lookup (Lookup to SF Object)