Googlebot first visits a page and records the access time, then on subsequent visits it checks the If-Modified-Since header to see if the page has changed since its last visit. If unchanged, Googlebot receives a 304 status code and knows it doesn't need to reload the content, but if changed it will load the page to get the updates. Status codes are logged to help sites understand if and when content is being recrawled by Googlebot after changes.