According to wikipedia “The 404 or Not Found error message is a Hypertext Transfer Protocol (HTTP) standard response code, in computer network communications, to indicate that the client was able to communicate with a given server, but the server could not find what was requested.”
What happen is that the server could not find the file that are requested by the server. There are a few causes for these and these can be easily fixed.
There are common few fixes like refreshing browser, clear cache and cookie or amending .htaccess file.
For woocommerce site, I have found the cause in 99% of the case to be cause by Permalinks. Just by matching the Url in the browser and the setting of your Permalinks under WordPress–Settings>>>Permalinks, should fix the error.