//--------------- HTML:

<form method="post" action="uebung_01.php">
	<input type="text" name="name" placeholder="Name eintragen">
	<button type="submit">Senden</button>
</form>





//--------------- PHP:

<?php
if( isset( $_POST['name'] ) ){
	echo '<p>
		<span class="fett">Ausgabe:</span>
		<input type="text" name="ausgabe" value="'. $_POST['name'] .'">
	</p>';
}
?>