Is this the floor at ground level (as in US usage) or the first floor above the ground (as in the UK)?
In the UK we call this the 'Ground Floor', the level above this would be the 'First Floor' and so on.
ground floor: térreo. But primeiro andar is used interchangeably with térreo, unless the "térreo" isn't at the level ground (as quoted, if there is a garage at the ground level).
In Portugal it appears to be more common to use "rés-do-chão" or "R/C" for ground floor and then "primeiro andar" is the first floor, above the ground floor - like in the UK. So, in Brazil it is the US way, but in Portugal it appears to be the UK way.
Not in Brazil. Usually "primeiro andar" is the first floor above the ground, and you must press the number 1 button in the "elevador" (eleva'dôr) to reach it.
The ground level is the "térreo" and you must hit the button "T" (or 0 in some modern buildings) to reach it.
The verb "to live" is mixing me up so much because in French...Italian...Spanish...moro would be related to "to die". :-P
Its similar in Portuguese. Eu moro - i live, eu morro - i die. The pronunciation is different ;)
We dont use "piso" so frequently, but andar.... if you go further, you'll see another answer which is more complete