This is a WordPress plugin, meant as a starting point for developers to tweak CoCart using WordPress filters and hooks.
You will need to be using CoCart v2.0.0 and up before applying any tweaks.
Create a /co-cart-tweaks/ folder in /wp-content/plugins/ and simply drop the co-cart-tweaks.php file into it. Then go to the Plugins page in your WordPress dashboard and activate it.
Open the co-cart-tweaks.php file and take a look at the __construct() function. You will notice that all the calls to add_filter() and add_action() are commented out. So, at the moment the plugin does nothing even though it's activated. To enable a filter, simply uncomment the appropriate add_filter() or add_action() line, but please make sure the corresponding function further down in the plugin's source has been adjusted to fit your needs.
Most of the examples in the plugin's handler functions will need editing before they can be used.