Is your car pre-wired for an amp? That would be the first thing on the list. You, someone you know, or a car audio shop will need to run wiring from the car battery and the pre-outs (red and white plugs) from behind the head unit before you can do anything (ported vs unported) .
What kind of 'truck' is this going in? Sub boxes will vary between one that is in an enclosed trunk or in open air. To add some bass to open air, I would go with two 10's or one 12 in a custom built box (each sub will have different specs for the best box that will put out the best bass.
When you are looking at amps and subs, look for the 'RMS' rating, not just the peak power for amps and subs. One amp may have 500 peak power amps, but an RMS rating of only 100. The RMS is basically the 'usable' 'good' wattage for the amp or subs.
From there, match up your amp with your RMS rating on the sub(to keep from blowing it). Typically you don't want the RMS rating on the amp to exceed the RMS rating for the sub(this would equal a blown sub).
My old set-up I was running a Presicion Power Powerclass 650 amp. It was 6x50 (ran my mids, highs, and subs with this) watt amp and I bridged it for the two subs and was pushing 200 watts(about 150 RMS) per speaker on 2 JL Audio 12" subs in a custom built ported box to match the specs of the subs for some DEEP bass .
I am a fan of JL Audio, Rockford Fosgate, Kicker Comp, Infinity......
Go here--> http://www.crutchfield.com/?evar16=Header:Logo they are very good with 'beginners' and there is a lot of good info here on building a car stereo....they also sell books and things to DIY.
Hope that helps....good luck!