how would i go about installing my sub and amp?

Do a search, man. You've got 37 posts, you're experienced enough to know that.

get wiring: power, ground, remote. RCA's that go from the hu to the amp (how many depends on the # of outputs and the # of channel on the amp that you want to use).
put a fuse within 12in of the battery for the power wire.
ground wire should be of same gauge and no longer than 3 ft. mount it to a good ground of the car
run the remote wire from the amp to the hu's remote turn on wire(won't hurt to fuse also, close to the hu)
run your RCAs from hu to amp
mount amp in good location, not anywhere it can be covered by anything or crushed.
connect amp to subs. (would vary depending on how you should wire it to get the most out of the amp.)
What are the amp and sub(s) specs. ?
do you have an enclosure for the subs?
where do you want the amp mounted?
More info would help answer your question

im not sure the specs of the sub because it was an old JBL 12" that i found in my back room. i was thinking of munting the amp maybe under the back fold down seat.
:EDIT: since im on the subject what about door speakers?

I don't know about the sub but most likely it would be 4ohm svc(single voice coil)

If you mount the amp under the folddown backseat, if you fold doen the seats you will crush it with the seat.
Do you have the flap behind the backseat? you can mount it there. I looked at your site(clean looking X) I'm not sure you will be happy with that box,looks a little small(volume wise I mean)

What do you need to know about the door speakers?
Are you using the stock wires? Do you have the hu installed already and connected to the stock speakers?
you can just remove and replace the stock speakers, or are you going to add a amp to them as well?

well what i want to do is replace the 2 back door speakers with alpine, and thats as far as i got. what exactly is the hu ?

hu = head unit

ok since there stock back speaker, couldnt i just replave them with alpines?

anybody everthink of adding 2 more speakers in the trunk space, like with a custom box or something, i want to do that also

yes, just replace them
you will have to cut off the stock speaker connector though(check a wiring diagram for proper connections
usually the 4 speakers are decent for most and the radio usaully only has 4 outputs(besides rca sub outs)