The easiest thing to do would be to go to your local car audio shop, or even Best Buy or Circuit City and tell them you need a reciever installation kit and wiring harness for a '94 Z-28. The kit will likely cost you between $12 to $18. The wiring harness from $8 to $12. You can also find them online for a little less, but with S&H plus the 3 to 4 day wait, the savings may not be worth it. The kit will mate your H/U to your factory radio opening and the wiring harness will allow you to plug right into your cars wiring (for power, ground and spkrs, etc) without having to cut any factory wires (big no no).
If you're also installing the amp and subs, then the amp kit Jeremy mentioned works the same way (if you don't have all that already). It will give you everything you need to hook up an amp to your system (in most situations). When you route your power wire from the batt to the hatch try to find a factory hole in the firewall to go thru. I believe the '94 has one towards the top passenger side of the firewall ( I'm an old
camaro junkie). Then route it underneath the carpeting along the pass side of the car untill you get to your cubby hole in the back. When you route the RCA cables, run them down the driver's side in the same manner (avoids interference from power wire). The blue wire, your "remote turn on" wire should go down the pass side with the power wire.
When hooking up the ground wire from the amp be sure to find a solid metal structure to bolt it to and clean any dirt, paint, etc off of it so you have a metal to metal connection. If you want to spray paint over it to avoid rust after it's hooked up and tested, be my guest. Don't put the power wire fuse in until everything is hooked up and connections are double checked to be correct.
I think Jeremy covered everything else pretty sufficiently, so I'll pipe down now. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
God bless you, hope it goes well. Come back if you run into problems.