Fat Free Cart plugin is an extension of FatFreeCart. With FatFreeCart Plugin you do not have to generate or paste any code in CSS or HTML of WordPress
Option 1 - Manual Install
Download plugin zip file from the http://www.FatFreeCart.com/wpplugin.html and unzip contents in wordpress wp-content/plugins folder.
Option 2 - Word Press Plugins Add New Plugin Submenu
Download plugin zip file and store it in a local folder. Select the zip file within the plugin within the "Add New option" in the wordpress plugins section.