how to add input value to session using php

I'm getting the question_id from db and I'm showing it in the input field. I want store that input value also in the $_SESSION.

How do I do this?

My code:

<div class="questionfun" onclick="return ChatLoginMax(event, <?php echo $chat_question_id; ?>);">
  <a href="javascript:void(0);">
    <p><?php echo $chat_question_title;?></p>
  </a>
</div>

<input type="text" id="chatquestionId" name="chatquestionName" value="">
    <?php 
        $_SESSION['session_name'] = $_GET['chat_question_id'];?>

Js:

function ChatLoginMax(event,chat_question_id){
   $("#chatquestionId").val(chat_question_id);
}