Ok, like i promised in a previous post of mine, talking about working with JSON and JMeter, i will discuss using the JSON response for extracting specific values, to be further used in the test script.
Now, there is no rocket science in this. Sending an HTTP Request with a JSON string as payload, will return a JSON string also, built on the same convention as already discussed. Now, the only thing you need is to extract the information you need from this response. I consider the Regular Expression Extractor to be the best option.