The best way to accomplish that is to use POST which is a method of Hypertext Transfer Protocol https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods
index.php
<html>
<body>
<form action="site2.php" method="post">
Name: <input type="text" name="name">
Email: <input type="text" name="email">
<input type="submit">
</form>
</body>
</html>
site2.php
<html>
<body>
Hello <?php echo $_POST["name"]; ?>!<br>
Your mail is <?php echo $_POST["mail"]; ?>.
</body>
</html>
output
Hello "name" !
Your email is "[email protected]" .