Rarible displays listings from the following marketplaces: OpenSea, X2Y2, LooksRare, Sudoswap, Objkt, Versum, Teia, Fxhash and ImmutableX. A blockchain is like a gallery where your art is stored, and a marketplace is a platform that exhibits your art and enables you to create, sell, store and purchase other art that is exhibited on the platform.
If you create an NFT on a marketplace other than Rarible, it will appear on Rarible once the gas fees for the NFT has been paid. If you list an NFT through the "lazy minting" option, the gas fees for your NFT will only be paid once the NFT is sold as the buyer is liable to pay gas fees for minting. This means that your NFT will only appear on Rarible once your lazy minted NFT has been sold or transferred.
The same concept is followed when you create an NFT on Rarible. Your NFT will appear on other marketplaces that aggregate listings from Rarible once the gas fee has been paid or once the lazy minted NFT has been sold or transferred. If you would like to learn more about lazy minting, you can follow this guide: Lazy Minting on Rarible.