. It's alright, we were all the same way, once.
Well, it depends what you are doing with the other motors.
If the other motors are part of the 4 wheel drive, then you can fit two motor wires into one slot and the 2 motors of each side run together.
But if your other motors are on an arm to need to function with separate commands, then you simply need to daisy chain another motor controller to the system you have set up right now. (Similar to how you daisy chained the servo controller, do the same with a 2nd motor controller).
If you are using RobotC, be sure to make the proper changes in the Motors and Servo screen when you set up the Motors and servos for the system.