Its very easy to overclock.It is even easier to overclock black edition cpus.You have to increase the CPU multiplier.Thats it.Also hundreds of guides are available online for advanced overclocking.
A decent 500-600Mhz OC is easily achievable.And yes you would see difference.
but if I overclock too much,does it blow or damge my CPU or Mobo or just restrart my PC to change settings?
You would get signs like frequent BSODs,freezing etc.Damaging your CPU is extremely unlikely because it would just restart and set the system to default.