Ok, here we go.
3 channels means that one is for throtle, one is for steering, and one will help to keep the signal strong. The on/off switch goes between the battery and the reciever. Typicaly channel one will be for throtle and channel two will be for steering, your reciever should be labled. Just follow directions. When you put your servo horns on your servos hook them up to the reciever and batter and turn everything on w/ the radio. Let them center so that the horns will be in the right position. Odds are you won't get everything perfect the first time. It normaly takes me acouple tries untill I get the hang of it. Just work with it and play w/ it untill you get things lined up right. When you set up your throtle//brake follow directions and make sure that in idle the carb is closed(it will be barely cracked for idling when it's closed and the idle screw is set right.) and make sure your brakes are opened up. Then make sure your brakes engage under brake and your carb opens up under throtle. Then do a run over of your steering and make sure it's set up right. You can use the throtle/brake cables and the trim adjustments to center everything. Once it's centered use the end point adjustments to set the servos so that they will stop on their own instead of the car stopping them because the servo turned too far. Once everything looks good you can start things up and tune it from there. The biggest thing is to make sure the throtle is set up right so that you can do a proper break in on the engine.