The @ record is known as the root domain, or top level of your domain; like "nomadecommerce.com". This must always be an "A (address) record" which will contain the IP number of your site. Your project manager will provide you with the IP number when you are ready to go live.
www record, or other subdomain record.
The "www" part of your domain is known as a subdomain. If you are using Nomad for your entire web presence then this will point to your root domain. If you already have a corporate site which will remain, then the storefront will go to a subdomain, for example "shop.nomadecommerce.com".
Subdomain records can be either the CNAME (Canonical Name) or A type, but not both. CNAME records point to another DNS record, usually that of the root domain. It only makes sense to use a CNAME record when Nomad is your primary or only web presence, in which case you will set it to your root domain; like "example.com". If preferred, or if your Nomad storefront is on a subdomain (other than www), an A record is used.