PHP front-end and background transfer? What to do with it

PHP front-end and background transfer?
How does the front end pass data to the background? How does the background receive data from the front end? With Json_encode ($A)? How does the background send the data back to the front end?
$.post (', {' QNumber ': qnumber},function (data) {

}, ' json '); What does that mean?
------to solve the idea----------------------
$.post, which means you send data by post
After the first parameter, the background processing page, use $_post to get the data you passed
{' QNumber ': qnumber} background page obtained with $_post[' QNumber ']
After the background page processing is finished, JSON outputs the page you want to return to the front end
Such as:
$return [' Status ']=1;
$return [' msg ']= ' Operation succeeded ';
echo Json_encode ($return);
------to solve the idea----------------------
How does the front end pass data to the background?
The browser sends data to the background in a GET or post manner, and the background is received as normal get or post

How does the background send the data back to the front end?
Of course, according to the format required by the front-end sent, who call you a service party?

$.post (', {' QNumber ': qnumber},function (data) {}, ' json');
Notifies JQuery to interpret the returned data as JSON
But this notice PHP is not received. So PHP can only return the data according to the prior agreement

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