How to connect php and html?

Question

PHP

How to make it read what is in the input, and how to make a variable or something, everything about this php is generally vague.
<input type="number" value="" name="fact">

<?php    
   $fact = ["fact"];
?>

Answer 1

For example so.
example.php file:

<form method="POST">
    <input type="number" value="123456789" name="fact">
    <input type="submit">
</form>
<?php 
    $fact = isset($_POST["fact"]) ? $_POST["fact"] : '';
    echo $fact;
?>

Run the web server in the directory where the file was created, for example, with the command:
Open the page 127.0.0.1:8080/example.php in the browser , after clicking the send data button on this page, the number 123456789 will be displayed.