[Update Mysql from text input (pdo)]

Sorry if this sounds like a noob question (  ), but how would I go about retrieving data POSTed from a text input field (sample below), update the respective row (WHERE id=1 for example) and then display the data in the same input fields again for ease of editing (all-the-while using PDO of course  )?

<form action="form.php" method="POST">
   <input type="text" name="header1" placeholder="Header text here">
   <textarea name="summary1" placeholder="Summary text here">
   <input type="submit" name="submit" value="Update Info">   
</form>