Well assuming you dealt with the mechanics there are usually 3 basic things:
-controller
-inputs (sensors)
-outputs (motor drivers, servos, displays, etc.)
THat's for autonomous. If you want RC, the inputs and controller become combined since the receiver is the one receiving the radio signals and outputting the control pulses to the motor drivers. CHeck out your hobby store for an RC transmitter and radio receiver. For the motor drivers you can use the speed controllers for RC, or you can go out and build or buy ones used for robots (they are printed circuti boards and stuff).