How to write form data to file?

Hello!
I have the following question: is there a website, or rather a template to bootstrap
It has a get started button, pressing which opens the registration form. I need the data entered in a form recorded in a text file (or csv)
For this, the code page is the form attributed action="func.php"
In func.php:
$source = $_POST['email'];
$file = "file.txt";
$Saved_File = fopen($file, 'a+');
fwrite($Saved_File, $source);
fclose($Saved_File);
?>

But nothing is working + I can not understand how to make closing the window after pressing the button.
If anything, the address at which the page is located 188.226.157.111

Thank you for your help!