How to make JSON data from JSON.stringify accessible by PHP

There are two parts to what you need to do:

1. Send the JSON to the server.

2. Decode the JSON into a PHP "associative array".

The first part can be done by submitting a form or using ajax to send a POST to the server. If you're not using any libraries, you'd use XMLHttpRequest to do that, but all of the major JavaScript libraries have convenience functions to make it easier. Since the easiest way to send the JSON string to the server is by using the standard multipart form data encoding, be sure to encode the JSON string using encodeURIComponent. So for example:

var xhr = new XMLHttpRequest(); // Older browers may need some special handling when creating the object
xhr.open("POST", "/path/to/your/page");
xhr.send("jsondata=" + encodeURIComponent(yourJsonString));

Since you've said you're using jQuery, you can use ajax to post the data to the server:

$.ajax({
    url:     "/path/to/your/page.php",
    type:    "POST",
    data:    {jsondata: yourJsonString},
    success: function(data) {
        // Handle successful post here, use `data` if your PHP
        // page sends a reply
    },
    error:   function() {
        // Handle error here
    }
});

The second part (receiving the JSON and decoding it) is done by accepting the POST variable (jsondata in the above) and decoding it via json_decode.