Fullscreen theme issues

I’m trying to install the Fullscreen theme by Graph Paper Press (https://graphpaperpress.com/themes/fullscreen/), and I tried following the install instructions but there is a step in which I need to change the permissions for a cache folder, and that folder doesn’t exsist anywhere in my theme’s folder. There is also no timthumb.php which I understand needs to be there.. Therefore there are no thumbnails on the home page as there should be. this is the site:
https://www.focus-prod.com/wordpress

I tried downloading the timthumb.php file and putting it in the theme/fullscreen folder, and also tried creating a cache folder and changings its permissions, but that didn’t do anything.

Please help! Thanks