Sorry! I got off on a tangent there and forgot the flip-flop..
http://www.talkingelectronics.com/projects/5-Projects/Projects16.html
In general, I find talkingelectronics is a very resourceful site for neat ideas. BTW, welcome to the forum!
An important detail (I think).... there are
three forms of this circuit
The above is an example of an astable multivibrator - but there is also a monostable and a bistable version. The bistable is what I would call a flip-flop.
The difference between the three is only with two components.
The astable version has two capacitors (as shown in the above diagram). The transistors take turns charging and discharging the capacitors. It has no stable state and will start off on its own because of subtle differences in the components.
The monostable version replaces one of the capacitors with a resistor. With this, the circuit will settle in one particular state. It then requires a 'trigger' on one of the transistors to start the charging cycle of the remaining capacitor. Once this cycle is complete, the other transistor will turn back on, returning it to the original state - and the circuit will stay in this state until another 'trigger' pulse.
The bistable version has both capacitors replaced with resistors. It has two stable states. Once one transistor is turned on, the other is off. The state can be changed by a trigger to the appropriate transistor - and the state will stay that way until the opposite trigger is applied.
A bistable multivibrator can, therefore, 'remember' a particular state while ever there is power applied to the circuit.
There is a variation of the bistable is where an incoming trigger pulse can be steered to change the state. One pulse will change it over and the next will change it back. This is a simple divide by two function.
You can go from there.........