as far as i get it if you tap onto the mike it generates a short pulse train burst !if the opamp has enough gain! that multiple re-triggers the 555 that will power the um3561 until the cap charges to apx. 2/3 Vcc or Vdd e.g. 8V incase of 12V supply
everything to the left from pin-2 of 555 ic must be tuned experimentally - or in other words - might fail to work as the designer of this circuit intended e.g. you need to match C1,R1,R2,R3,R4,VR1,VR2,R5 with your actual mic. opamp and NPN -- nothing impossible -- but i guess you do need to do this under supervision and guidance of some more experienced person - - - or simply put if you see your led blinking when tapping at mic. it's doing what it should