User Activity

Hi, I need help to auto populate assignment group field(mandatory) based on caller's(logged in user) company. If caller belongs to 'XYZ' company then assignment group field should be auto populated with a particular group. This should happen on form ...
I have created a report. I want that only users with a particular role should be able to able to read that report.How to achieve this funcaionality.
Whenever a problem is added on problem reference field on incident form. Current incident gets added to related list "Incidents" on related problem record. How is it happening?  Also how can i implement same process for change request that when a cha...