Ok rockford fosgate made the HE2's in two different types. 4 ohm and 2 ohm. Depending on which model you bought the following is the correct answer.
Keep in mind you can wire these down to a .5 ohm but I would not reccommend it being that most amps will over heat and shut down. I recommended the 2 ohm option, but you it can still shutdown if your amp is not 2 ohm stable, so you will have to try and see. If you tell me what kind of amp you have it'll be easier to recommend.
(Honestly it is confusing to explain typing out, but rockford has made it fool proof for you)
2 Ohm Subs 4 Ohm Subs If you do not have an amp, I suggest buying something that is 2 ohm stable, if not stable below an ohm. If you can find something stable below an ohm, they will thump the loudest. But at least 2 ohms I recommend.