How to activate service on my iphone 5?

I just got it today and i've done the set up but it still says no service and my old 3gs still has service how do i fix this

I would contact my carrier if I were you and talk to them about it

Contact the service provider. They will need ICCID of the nano sim to activate it and transfer the phone number. It's the same procedure as it was to transfer from regular to micro sim