Re: 95 civic dx d15b7 to d16 vtec
Move EVERYTHING from the EX to your DX shell... D16 engine, wiring harness, intake manifold, throttle body, etc. Plug in the EX engine harness to your DX chassis harness at both shock towers. Follow the VTEC solenoid and pressure switch wires back to the plug at the passenger side shock tower near the fuse box and battery tray... you will see that the blue/black and green/yellow wires do not continue past the plug on the chassis side and into the interior of the car... there are two brown rubber plugs in the holes instead. Run new wires from the shock tower plugs to the ECU and pin them in the proper locations... I suggest getting a few donor wires from both plugs at your local Salvage yard. VTEC solenoid is A4, VTEC pressure switch is D6, plug in the EX ECU (yes, you HAVE to have it to make VTEC work).
Advice: You have asked some really BASIC questions here... I suggest you either seek assistance from someone who has done this swap successfully before or spend a ton of time researching this for yourself before diving in... be logical about your actions and decisions, and be thorough. Take whatever time is necessary... rushing the project just to meet a deadline usually doesn't end well for you or the car.