PHP Code:
<?php
  
if(isset($_POST['box'])){
    echo 
"the checkbox was checked";
  }else{
    echo 
"the checkbox was not checked";
  }
?>
<form method="post">
  check this --> <input type="checkbox" name="box" />
  <input type="submit" value="go" />
</form>
if you can't figure it out from looking at this example, run it on your server and try it out.