Flotilla hosts spaces on the Nostr protocol. Nostr uses "relays" to host data, which are special-purpose servers that speak nostr's language. This means that anyone can host their own data, making the web more decentralized and resilient.
Only some relays support spaces. You can find a list of suggested relays below, or you can host your own. If you do decide to join someone else's, make sure to follow their directions for registering as a user.