You have to execute a system setup first using special one-off token. Use you favorite GraphQL client and execute following graphql mutation against your production server:
This mutation will create a superadmin with given credentials and returns a login token. Don't loose it, otherwise you won't be able to login!
First you have to choose a S3 provider. You can decide between hosted services like AWS S3 or you can self host your own S3 compatible storage.
After you choose the right provider, you just have to setup relevant S3 environment variables.