Let's say you have the following file structure:
In your index.php file, you would just use "include" as you normally would:
Just because the user can't access the folder, doesn't mean PHP can't see it.
If you wanted, you could use an absolute path, instead:
And if you're not sure of the absolute path, you can use the __FILE__ magic constant:
echo __FILE__; // echos the full path and filename of the current file