What do Google spiders do?

Google spiders, also known as crawlers or bots, systematically browse the internet to discover new and updated web pages. Their primary function is to "crawl" the content of these pages, following links from one page to another. The information gathered during this crawling process is then sent back to Google's servers to be added to its massive index. This index is essentially a giant database of all the web pages Google knows about. The option "Index and rank search results based on relevancy" is incorrect because while Google does index and rank search results, this is a separate process that happens after the spiders have crawled the content and added it to the index. The spiders' role is specifically the crawling part. "Add security certificates to websites" is entirely unrelated to the function of Google spiders; security certificates are managed by website owners and certificate authorities.