What a network announces, who carries it, and who buys transit from it.
An autonomous system is one network's routing identity: a number, held by an organisation, that announces blocks of addresses to the rest of the internet and says which other networks it will accept traffic through. Everything on this page is read from that announcement rather than claimed by anyone. The registry says who holds the number. The global routing table, as several hundred collectors around the world see it, says what it is announcing right now and which networks are carrying those announcements.
The neighbours are the interesting part. A network that appears to the left of this one in a routing path is carrying its traffic onward, which makes it an upstream, a transit provider it is almost certainly paying. One that appears to the right is being carried by it, which makes it a customer. A network with four upstreams and no customers is buying transit and selling hosting; one with six thousand customers is a transit provider. You can read a company's whole business model off this table, and it is one of the few places where that is legible at a glance.
Two columns here are worth more than the rest and are missing from most tools. RPKI says whether a prefix is cryptographically signed by its holder, so that networks which check can refuse a hijack of it. The IRR column says whether a route object exists, which is what large carriers filter on. A prefix announced with neither is working today because nobody is filtering it hard, and is one policy change away from being unreachable.
An upstream carries your traffic to everywhere, and you generally pay for it. A peer exchanges traffic with you directly, usually for free and usually only between your two networks and your customers. This page infers both from routing paths, so a network seen on both sides of different paths is shown as a peer rather than guessed at.
This counts what is being announced right now, not what is registered. Space that is allocated but not announced does not appear here, and space announced on your behalf by somebody else appears under their number.
It works, in that packets arrive. It is not protected: without a ROA, another network announcing your prefix cannot be told apart from you by anyone checking, and more networks check every year. A ROA is free and is created at your registry.