Do I need an amplifier for my subwoofer?

I'm purchasing a AudioPipe Car Audio APBP1255LD Dual 12" 1500 Watt High Performance Bandpass Enclosure for my car. My stereo has a bass output but i dont if it has nearly enough watts to power the 750w RMS the sub has. If i need an amp, do i need a mono or a 2 channel?

The fact that you're asking this question means you probably have no car audio experience. Be careful - retailers 'prey' on your type (nothing negative - just true)

The bass output from your stereo is most likely RCA ports, and the bandpass enclosure you're about to buy will have speaker wire terminals.

Also, the type of 'car' you have will help in determining whether or not you'll benefit from getting a bandpass box. If you drive a hatchback or SUV (some type of vehicle with open air space to the 'trunk' area) then a bandpass box may be a good choice.
If you drive anything with a separate trunk (separate/closed off air space) then a bandpass box probably isn't the way to go.

Are you going to be hooking this up or is someone else going to?

Yes you need an amp
Whether or not you get a mono or 2 channel amp depends on the impedance of the subs and whether they are single or dual voice coil.

Looking at what I found on that box (not very much info) it seems like that 1500 watts is both subs put together - not each sub individually. If that's true and there's only one terminal, then I'd suggest you go with a mono amp.