JSON.stringify turns a JavaScript object into JSON text and stores that JSON text in a string, eg:

var my_object = { key_1: "some text", key_2: true, key_3: 5 };

var object_as_string = JSON.stringify(my_object);  
// "{"key_1":"some text","key_2":true,"key_3":5}"  

// "string"  

JSON.parse turns a string of JSON text into a JavaScript object, eg:

var object_as_string_as_object = JSON.parse(object_as_string);  
// {key_1: "some text", key_2: true, key_3: 5} 

// "object"