under warrantee still, do I have to go only to a dealer for repair or oil change?

You can have your car serviced where ever you like just keep the receipts. Obviously the dealer will do the warranty repairs.

Warranty work is free at the dealer while independent shops will bill you for it. Other services can be done by independent shops but stay with reputable businesses and, as FOR said, keep your receipts if they relate to things that may go bad in the future. An oil change is a good example. If you don't have proof you had routine maintenance done at the manufacturer's suggested intervals, they may not perform some repairs under warranty and bill you for them.