Host what?

A relay is where posted content is stored.

The basic premise is that like most social media you probably won't be able to upload 1 GB files. This is true of Twitter, tik tok, Instagram, discord and even some file-sharing platforms. To upload big files like movie length videos you probably will have to pay for that privilege like you do on discord, and twitter but if you're only doing 30 second long videos you will probably be OK unless it's 4K or something. Nostr is simple, you NSEC/Key is your password, your Npub is your handle but you can use NIP-05 services like these to get easier handles.

Nostr Plebs | Get a Nostr Address (NIP-05)

Nostr Plebs is an easy way of getting a NIP-05 identifier/Nostr Address and other Nostr services, made by Bitcoiners, for Bitcoiners.

NIP-05 — Nostr Address Verification

Get your verified Nostr address. Simple, fast, powered by Lightning.

https://orangepill.dev/nip-05/ If you have a website you can make a custom one.