Static Cookie free subdomain

I am using yslow. I have researched this issue and I am not finding any resolution. Usually when I have an issue it is a simple fix. So here is is I have found root wp-config.php and have made the necessary changes within it now the next step per reference: https://www.xpertdeveloper.com/2011/07/wordpress-cookie-free-domain/

is “Please make sure that you have used “bloginfo (‘template _directory’)” to load your static content in theme files.”

What does this mean I have researched wordpress to how to do this but I am not finding an exact reference to go by. I appreciate any help.