REM needs to be hooked up for the amp to turn on and off when you turn your car on and off. If you just want to test, you can connect the remote wire to the same source as the main power but this will leave your amp on even when your car is off, draining the battery.
If you're using a factory head unit, you should splice the REM wire right into the power antenna. If you don't have an power antenna or if your head unit doesn't have a REM wire output, you can use the power from the cigarette lighter or any other power source that turns off when your car is off.