Not to nitpick, but BGP is a routing protocol, their issue had something to do with DNS going down due to a disconnect between their datacentres.
pretty decent explanation here - https://www.theguardian.com/technology/2021/oct/05/what-caused-facebook-whatsapp-instagram-outage
If you want a easy to understand analogy, imagine that DNS is a post office, it is able to identify a persons name with a street address. BGP would be the delivery driver getting your package to the destination.
In realworld, DNS resolves hostnames to IP addresses, so when you type in google.com into your browser, DNS resolves the hostname to an ip address. Your ISP will then use BGP routes to see where it is learning the route from and steer the packet accordingly.