I am sorry that I don't have the ability to post diagrams however you can find what you need in various ARRL (American Radio Relay League, ham radio) handbooks.
It is my understanding that the varactor (or other) diode can be placed in parallel with the other capacitor(s) in an oscillator circuit - and that the varying voltage (such as that from a microphone) will modulate the frequency. The amount of shift or deviation is dependent on the circuit and of course, the diode. With this little bit of information you might simply look for information on various RF oscillators - knowing that the diode is in parallel with the capacitor in the tank circuit.