I am new here, but I have a 2006 1.2 Dynamic, so hope this is of help
My Panda came with 2 keys : - a key and plipper for remote central locking, and a separate key that does central locking but only if put in the door lock in the driver's door.
If you only have the key for the door lock, then it is possible that at some time in the past the plipper has been lost or broken. I think you can get a new plipper from a Fiat dealer but it is likely to be very expensive and might not be worth it.
The door key should open all the doors including the tailgate, but there is a known fault with the tailgate where a faulty microswitch causes the tailgate not to open (this fault and the repair is covered in other threads). This fault has affected my Panda, but the tailgate still opens by putting the key in the lock, and it is not worth the fairly high cost for me to replace the microswitch