You got back a JSON string either as a response from a REST service, passed through from your visual force page via remote action or passed from your lighting component to your apex controller, now how do you parse this information? For simple JSON structures Salesforce can automatically parse them for you. There are tools online that would generate apex classes from the JSON string that would assist in parsing the JSON input.
It is good to get back to the basics and understand a little bit how the JSON string is structured and how the parsing is done.
What is JSON? JSON is the acronym of Javascript Object Notation and is a lightweight format that is used for data exchange between servers and modern applications. It is based on a subset of JavaScript language (the way objects are built in JavaScript).