function get_option($option_name){
     // SELECT option_value FROM ayarlar WHERE option_name = $option_name
}
function update_option($option_name, $option_value){
     // UPDATE ayarlar SET option_value = $option_value WHERE option_name = $option_name
}

<form>
     <input type="text" name="site_name" value="<?=get_option('site_name')?>">
</form>

if($_POST){
     update_option('site_name', $_POST['site_name']);
}