Yes, you open the file in read mode for nothing, unless you really do want to capture the file pointer value for some inane reason (which I shall assume you do).
You declare $new but do not use it, while $news hasnt been defined.
I dont understand your comments as they are not in English.
Then you use the marquee tag 😛
Anyway, here's a guess:
<?php
if (isset($_POST['submit']) && !empty($_POST['news'])) {
$filename = "text.txt";
// Datei aus lesen
$datei_lesen = fopen($filename, "r");
$datei = "$datei_lesen,9999";
fclose($datei_lesen);
// Neue Text einfügen
$news = "<marquee>{$_POST['news']}</marquee>,$datei";
// Mit neue Text Über schreiben
$fp = fopen($filename, "w+");
fwrite($fp, $news);
fclose($fp);
}
?>
<form action="editor.php" method="post">
<input type="text" name="news" size="50" value="">
<input type="submit" name="submit" size="50" value="Speichern">
</form>
<a href="ticker.php">see result here </a>