What do you need help with? If you have never done one before, there are plenty of step-by-step guides out there. Google is your friend.
If you need specifics for the Tahoe, there's plenty of help here. Be more specific with your questions.
Common questions relating to GM factory + sub:
1. How to run power from battery to luggage area?
Drill a hole in the firewall just above the brake pedal. Install a rubber grommet that fits well.
2. Where to ground the amp?
Either behind the factory sub (the plastic panel that holds the jack) or underneath the 2nd row seats there are a few bolts.
3. Wiring the RCA cable to the back?
There are wiring kits to either modify your harness, add an RCA port from speaker wire, or get an amp that can run speaker wire.
4. Which is the remote wire?
The blue one.