By using PLL the two frequencies say input frequency and the reference frequency of the VCO are compared and it sets to the stable frequecy.
Where ccp is Capture, Compare and pwm. where capture used to detect the raising and falling edge of signal and compare is interrupt that compares the changed value with the pre-set timer and pwm signal at that frequency.
you can choose the type according to your required application and what type of operation you want to perform.