Start with the wallet you already have
Nothing is created here. Your NextKey ID is derived from a signature, so the same wallet gives you the same ID on any machine, for ever.
Or take a name that is yours
The same key, on a name nobody can take back. A contract hands out one name per address under nextkey.eth and publishes your key on it in the same transaction — you pay for that transaction, and afterwards the name belongs to your address, not to us. You can point it at another resolver whenever you like.
This one needs Sepolia ether in your wallet, because you are the one signing it.
What a NextKey ID actually is
It is your published key, written so a person can handle it.
The ID is derived from the nextkey.pubkey key rather than issued alongside it. There is no registry, nothing is allocated, nothing is written to the chain for it, and there is nothing to lose — the same key gives the same ID to anybody who computes it, offline, on any machine. Every name that already publishes a key already has one.
It is not a secret and it is not a permission. The key stays in nextkey.pubkey and is what the arithmetic uses; the ID is what the interface says. Anyone verifying rather than reading compares the key.
What this does not give you
A lent name is borrowed, not owned. It belongs to NextKey, and the record on it was written by NextKey — which means we could take it back. Your NextKey ID does not change when you move to a name of your own: it belongs to the wallet, not to the name.