can anyone explain about phase locked loops....i know what they r.......but what stuff r they used for?

 

Frequency synthesis, where one base frequency can make any other frequency digitally. If the base frequency is hyper accurate, so will the derived frequencies.

FM discrimination. There are other ways to do this, but PLL tends to be higher fidelity.

Pulling a frequency out of noise, relates to the discrimination issue. Tends to make better AM radios because of it.