You can add the variable in the link to the next page:
<a href="page2.php?varname=<?php echo $var_value ?>">Page2</a>
This will create a GET variable.
Another way is to include a hidden field in a form that submits to page two:
<form method="get" action="page2.php">
<input type="hidden" name="varname" value="var_value">
And then on page two:
$var_value = $_GET['varname'];
$var_value = $_POST['varname'];
//Using GET, POST or COOKIE.
$var_value = $_REQUEST['varname'];
Just change the method for the form to post if you want to do it via post. Both are equally insecure, although GET is easier to hack.
Hope it helps!!