I'm not completely sure I know what you mean by page address. But for example, if you have:
www.example.com/index.php?page=x
and
www.example.com/index.php?page=xy
Then you can create a conditional statement like:
if((!empty($_REQUEST['page'])) && ($_REQUEST['page'] == 'x'))
{
// Show page x
}
elseif((!empty($_REQUEST['page'])) && ($_REQUEST['page'] == 'x'))
{
// Show page xy
}
But more likely, you'll want to accept multiple values for 'page' and pull them from a database or file.
Then you'd want to simply check for page, validate page with whatever parameters you require, then load page from DB or disk, and display.
if(!empty($_REQUEST['page']))
{
// Do whatever with $_REQUEST['page']
}
else
{
// Default behavior
}