If your going to use a form, make a form field
<form action="query.php" method="post">
<input type="text" name="param">....
//Call the parameter
$sql = "SELECT * FROM table WHERE param = '".$_POST['param']."'";
Or just a link...
<a href="query.php?param=param">query</a>
//Call the parameter
$sql = "SELECT * FROM table WHERE param = '".$_GET['param']."'";
Lots of different ways you can do this...