Upon activation, the plugin will configure itself with the basic settings. Any categories that you have on your WooCommerce store that do not have a thumbnail set will then start displaying any available product thumbnails inside the category.
There are a number of options, these can be found in WooCommerce -> Settings -> Products -> Auto Category Thumbnails.
Thumbnail Size sets the image size that the plugin should use when displaying the thumbnails. Defaults to shop_thumbail, but shop_catalog may be a better option for some themes.
Go into Child Categories makes the plugin look in child categories too, useful if you have products buried in quite a deep category structure.
Random Thumbnail tells the plugin to pick a random product thumbnail from those it finds every time the page loads – otherwise it always uses the first one it finds.
No screenshots provided