can Anyone explain this circuit to me what each component do ?
assuming there is a microphone in place of the buzzer
and assuming that the transistor is 2N3904

 

Somehow, all of the forward slashes were removed from your link to the schematic.

This looks like a homework assignment. Is it?

 

No i just used this circuit as a sub circuit in a project I made I found the output suitable and focused on the programing schema and now i need to understand more thing about this circuit ..

 

here is the circuit

 

the question is resolved

 

Common emitter amplifier for a knock/sound sensor, or similar purpose.

 

The original schematic is WRONG. It uses a piezo buzzer that has an oscillator inside that shorts the base of the transistor to ground.
Instead it should use a piezo transducer that works as a microphone and does not conduct electricity.

If you use a dynamic mic (coil and magnet) then it will also short the base voltage of the transistor to ground. If you use an electret mic then the DC supply voltage for it will be too low for it to work.