Copy the files from this plugin into the corresponding folders on your installation, as mentioned below:
Copy the CWTip/gateways/cwtip.php file into your installation's /module/gateways/ folder.
Copy the CWTip/gateways/callback/cwtip.php file into your installation's /module/gateways/callback folder.
Copy the CWTip/gateways/cwtip-sdk folder into your /module/gateways folder.