Relays store notes, notes you want to read. If you don't run a relay, you'll need to use someone else's. who run relays filter out spam for you. To use their relay, they might want to charge you.

Hi! nostr.wine is a high performance paid relay that also gives you access to filter.nostr.wine that has additional features.

You can read more about the relays on their respective sites:

https://nostr.wine

https://filter.nostr.wine