Where do I put my c wire the un used or c wire for me is blue but where do I connect it to?
Include it in the nut with the red and grey wires in it

Given that the wiring diagram for your furnace says that the grey wire going into the thermostat wiring compartment is your C wire, we can connect the blue wire to the thermostat into the existing junction there to make it a C wire for your thermostat's use.  This is further substantiated by the fact the yellow wire in your thermostat cable goes off into the white wire in the compressor cable, which leaves the red wire in the compressor cable to return 24V control power back to the transformer, which implies that the red wire must be connected to the furnace's C wire.