Linh:
+12v= Direct connection to the battery's POSITIVE terminal. I would SERIOUSLY think about buying an amp kit from some reputable place like Best Buy, Circuit City, or a local Car Audio shop. Street Wires makes some good ones. If that is not an option, then at the VERY LEAST go to above stores and get an INLINE fuse rated for your amp. This is VERY important to your car's wiring if something were to go wrong. Be sure to use a heavy gauge (no smaller than 8 gauge) wire.
GRND= A direct GROUND to a spot within 12-24inches of the amp. This can be done directly to a METAL spot (preferably to part of the framework of the car) somewhere in the trunk area. Doing this correctly will keep any 'alternator whine' and other spurious noise from entering the system. Depending on the car, there may even be a factory ground somewhere in the trunk area. Be Sure to use the same gauge wire (or better) than your +12v.
Rem = Remote Amp turn-on. This is generally a BLUE wire (no stripe) that comes directly from your headunit. In some instances you can use the 'ANT' or Antenna lead from your head unit. This is (I think) a 5v power lead that only sends a short 'signal' to your amp when you turn on your head unit. This tells the amp to 'turn on'. The opposite is true when you turn off your head unit. This can be of a lighter gauge (12-16gauge is fine). If you don't have this hooked up...your amp will not turn on.
Also, make sure that you don't connect a wire to the REM that is 'always on'. In otherwords, make sure that when you turn the key to the 'off' position, that the amp shuts off. Otherwise, you will kill your battery.
Hope this helps (PM me if you have any more questions)
SupaDupaCheez