通过php中的ajax在数据库中插入数据

I am trying to insert data through Ajax

Can anyone help me .. I want to insert data in database using Ajax in php

My table name in database is post and my fields are register_id, post_data, time

 <form class="form center-block" method="post" action="actionpost.php">           
      <textarea class="form-control input-lg" name="post_data" autfofocus placeholder="What do you want to share?"></textarea>
      <button name="submit" >Post</button>
 </form>