Download the zip file.
Log in as the WordPress Admin of your website.
Navigate to Plugins > Add New to upload plugin
Choose the plugin file to upload.
Activate the plugin.
Note: Free WooCommerce plugin should be installed & activated before activating Woo Auction plugin. Also, Ajax add to cart should be enabled on WooCommerce -> Go to WooCommerce Settings -> Products Tab and tick Enable Ajax add to cart buttons on archives