basic php question...

hi guys... i've got a button that i want to select, and i want the app to process some logic, and then return the user to the page. my question is how?? something like base page: <a href="foo.php">button link"</a> foo.php -process logic -return the user to the base page, with the same querystring that was initially used to generate the initial base page foo.php doesn't have any display function, just the logic thoughts/sample php pages/psuedo code chunks... thanks