Cert Warden is generally used with a public CA. Public CAs will only sign certificates for public domains you control. This would not include something like localhost.
It is possible to roll your own CA and also user Cert Warden, but this is almost certainly not what you want (and adds complexity).
You're probably looking to create your own CA using something like openssl, but you would have to manually add the CA to every device's root trust store, otherwise you'll see trust errors.
Tl;dr:
Public CA: All devices will trust your certificates, but you are limited in the domains you can get certificates for.
Self-Signed CA: Get a cert for any domain you want, but your devices won't trust them unless you manually add the CA to each device's trust store.
