The NIP standardizes the communication between client and media servers. It allows to publish a URL with the data of your server and any client nostr must have a list (similar to relay) to add them, delete them, etc.

See, for example the URL of nostrcheck.me

https://nostrcheck.me/api/v2/nip96

Here is the draft of the NIP, it is already well worked out among many people:

https://github.com/arthurfranca/nips/blob/nip-95-contender/96.md