Okay.. will start from the beginning.
I assume you bought an AMP KIT, with power wire, ground wire, the blue remote wire, RCA Signal Cables, and all of the ends you need...
Here's something else you will need though...
Go to Advance Auto Parts, Autozone, any place like that... and purchase a line converter. It's about $20. I'll explain what this is for in a bit...
1st.) Take your power wire, usually red, and feed it from the POWER POINT or your POSITIVE point on your battery (LEAVE IT DISCONNECTED DURING THIS PROCESS SO IT DOESN'T ARC OUT. ALSO, MAKE SURE YOU CONNECT YOUR SUPPLIED FUSE. Hook it up within 6-8 inches from your battery or power point.) under the hood, through a grommet in your firewall or you might have to drill a hole through your firewall to push it through. Once that is through, run the wire under the panels along the side of your car back to your trunk, or wherever you desire to put your amp.
2nd.) Find a spot in your trunk, or a spot on your car where there is BARE METAL... you might have to grind paint off in the trunk area to get a TRUE, SOLID GROUND!... take the ground wire that came with your amp kit and bolt it down to your car.
3rd.) Now take your remote wire (the blue wire) and tap that up either to the PINK wire (ignition wire) under your steering column, or pop your hood and find a FUSE under your fuse box that ONLY GETS POWER WHILE THE CAR IS ON! (use a test light if you have to, and see what fuse gets power while the key is in the ON position, and NO power while the key is OFF)... pull that fuse out, wrap part of the stripped end of your blue wire around it, and replace the fuse from right where you had it.
Now it's time to test your amplifier to see if it powers up. Hook up the RED POWER WIRE to the BATT or 12V+ on your amp after connecting it up to your power point or your battery under the hood, the BLUE REMOTE WIRE to the REMOTE on your amp, and the GROUND WIRE to the GROUND or GRND on your amp. See if your amp lights up when you turn your car ON... if so, you've hooked that up correctly.
NOW comes the part with that line converter I mentioned earlier. Go to the trunk of your car where your factory 6x9s are and pull some of the slack wire down from them. Take the line converter and tap those wires into the 6x9 wires. (The line converter should have like 6 wires. 2 are worthless. the other 4 are usually in pairs of colors.. i.e. 2 of them are GREY, and two are GREY AND BLACK.. take one GREY and one GREY AND BLACK and hook those to one of your factory 6x9 wires and the other set of GREY and GREY/BLACK to the OTHER. Then you plug your RCA cables into the back side of the line converter and plug that into your amplifier accordingly. Now it's time to run speaker wire from your amp to your subwoofer. Positive to positive, negative to negative.
HOPEFULLY all has been done correctly and you will now have bass in your car.
I hope this helps.
I'm not responsible if you screw anything up though. Haha!