each speaker has a difference impedance(resistance) load. most speakers for car audio are rated at 4 ohms. some speakers are single voice coil and some are dual voice coils. depending on how you wire things you can create a different impedance load. if you hook up two 4 ohm speakers in parallel(the positive terminals are together and the negative terminals together) you will get a 2 ohm load. if you have a single sub that is a dual voice coil, you can wire it to create a 2 ohm load(refer to its instructions). the difference ohm rating on amps means that the amp produces different power at difference impedance loads(depends on how you wire your subs) the amp you bought is a mono bock amp meaning that the terminals that you hook your speakers up to are the same(should be two sets of + and - terminals). so if you hook up a 4 ohm speaker, the amp will output 230 watts. if you hook up a second speaker in parallel, the amp will output 338 watts. this is just the basics of what your asking, everything is dependent on your amp and sub combo. if you did not understand something, post back your questions.