Hi Ras,
1) To make your amplifier an oscillator, first you must determine which class of operation it will be.
a) Class-A is the most linear but since the transistor conducts all the time, it uses a lot of power and heats-up.
b) Class-B is with 2 transistors.
c) Class-C is when the transistor is turned-off most of the time and conducts heavily for a moment. It is very efficient but transmits many strong harmonics.
d) Class-D is a switching class used for power supplies and audio amplifiers, not radio frequencies.
e) I don't think there is a class-E, just the sim program you have with that name.
The class of an oscillator is determined by the transistor's bias.
2) To "close the loop" of an amplifier to turn it into an oscillator, the circuit can be Collipits or Hartley, deterined by whether its positive feedback is provided by center-tapped capacitors or a center-tapped inductor. I can't remember what it's called but you can also cap-couple its tuned collector output to its emitter input.
3) To FM modulate a high frequency oscillator you can connect a voltage-controlled-capacitor (vari-cap diode) across its tuned circuit. Frequently an ordinary reverse-biased diode will work. Change the voltage across the diode and its capacitance will also change, which changes the resonant frequency of its tuned circuit.
4) An oscillator is an amplifier with a gain of 1 or more and positive feedback so it can continue to oscillate without any extrernal input except supply power.
I hope this helps you understand and that I presented it all correct.