how to make form dynamic shape in php

we just write the form code in simple html:
for example:
<form action="action.php"method="post">
<input type="text"name="name"placeholder="Enter name">

<input type="password"name="pass"placeholder="Enter password">

<input type="submit"name="submit"value="Log In">
</form> 
at the top the action.php is the page were action will be done for this form
we write the code in action.php
<?php
if(isset($_POST['submit'])){
echo $name=$_POST['name'];
echo $pass=$_POST['pass'];
?>
as the action is post the isset me when the button will click name submit the that simply echo that code that we write in input in text at name this will show name and at password this will show password