A simple example of frequency and what it's measured in:
Frequency can be defined simply by putting one dot on a piece of paper. If you want more dots than you increase the frequency by writing more dots. If you take this example and apply it to a radio broadcast than you would be referring to signal strength. To increase the signal you would increase the frequency. When you increase the frequency the signal expands and the station can reach a wider audience. Frequency is measured in hertz.