The +12v input is the line going from your batter to the amp, use a low guage wire for this (lower is thicker, and thus higher amperage). It's very important to connect this to the correct side of the battery, although in my very drowsy state I cannot remember which side it is. Most likely the Positive (+) side because it says +12v...
The REM is the Remote Activation wire, and it connects to the 'ignition' wire going into the back of your radio deck inside your dash, or the remote wire coming out of your radio if it is newer, some have them. This tells the Amplifier when your car is on and off so that it does not turn on and drain your battery while your car is off for a long time.
The GND is the ground wire, and you attach a wire from this to somewhere on the frame of your vehicle. If you are installing everything inside your trunk, as I did, you might be lucky enough to have the antenna back there too, and this has a spot where it is also grounded to the frame, so just bolt it onto there. Otherwise you may have to drill a small hole into your frame, use sandpaper to clear away any paint so you can make a solid connection, and bolt it to the frame that way.
If it is a Mono amp, meaning it is meant to power just one Subwoofer, then it will have 1 set of inputs(that are actually outputs) for your subwoofer. I believe this is what you meant by the +ve and -ve. If it is set up for 2 subwoofers then it will have two sets, just choose one, it'll work either way. I have never heard a song that has bass coming out of just one side of the speakers.
There will also be 2 inputs that look like the Video/LeftAudio/RightAudio you would see on the back of a TV. I call them banana clips. This is the input of the audio(sound) from your radio deck to the amp.
Good luck on your project, and hope that everyone can hear you bumpin down the street from a long way off! >
