I think santos means, does it come with a remote control on the key. I believe they come with a remote key or a standard key that unlocks all the doors but not both. So if you have just a key turn the key in the lock and all the 3 doors open. As lunilupi says you will also have 2 buttons on the armrest inside 1 to open and 1 to lock.
You could visit a SEAT dealer and ask if it will take remote keys as they may have been lost by the previous owners and left with the one manual key.