I want to know steps of working of this circuit , but not clarification in links as I searched too much and I get the overall point ,but I need details ,as why does C1 charges and discharges ,the importance of the parallel capacitor of 100 uf and what is after the transistor is in cut-off region ?
The DC source of 9V may contain noise which you don't want to effect your circuit, capacitor are doing that job for you, the resistor 47k & 4.7k are for biasing the transistor and C1 allows AC noise through it to the ground, which otherwise would effect. The parallel C of 100uF is doing the same thing but on whole circuit level i.e. removing AC signal from the battery. its a common practise of doing.
It's a simple oscillator using the transformer to provide phase inversion. As C1 charges it changes the bias condition of the transistor and hence the oscillator frequency. It might be a door bell chime or a sound effect generator.