Digital certificates in https vs device

I am new to digital certificates and it's various types and applications. What I know/assume as of now is in https communication, a CA will issue a certificate which will basically contain a public-private key pair which the Server and Client will use to communicate securely. And authentication will be through conventional password like mechanisms. Please correct me.

Now in the context of device certificates, does it serve the purpose of authentication only, if yes, then how? or it also serves the purpose of secure communication by means of public-private keys. How it is used. How does a server determine the authenticity of device?

And in https there is only one certificate that a Server/Host and it's Clients will have, whereas, in device based it's issued per device. Am I right?