You need to use the divide and conquer approach.
(FluBBa's confusion comes because mHz stands for "milliHertz", or 1/1000 of a Hz. For audio frequencies you would use plain Hz or KHz [kiloHertz]. FluBBa [reasonably] assumed you meant MHz or MegaHz, which is millions of Hz, usually used for RF signals and way beyond the iPads capability.)
First learn how to write a basic app that displays a number.
Next read the microphone and determine when there is a signal.
Lastly, perform an FFT to turn the signal samples into a set of frequencies.
I suggest you get something like MatLab to experiment with the signal processing.