Flyback transformer - ambiguous schematics and other issues
This part of the circuit is just a simple 555 astable with variable mark/space ratio.


The capacitor, along with the resistance values sets the frequency. The transistor is there to drive the mosfet which simply switches the current on and off through the primary of the transformer. The transformer steps up the voltage depending on the turns ratio.

The capacitor will be .01 microfarad (or 10nF as Andy correctly gives). By using a 100pF capacitor the oscillator will run at too high a frequency (100 times more than the original design).

I also agree with Andy that the transformer (and its design/construction) is your real problem.

My real concern about this question is that if your knowledge of electronics is this limited then building this type of circuit could be fatal. High voltage is not not an area a novice should tamper with.