What is the meaning of these sections? I observe these field for port 443 and in particular I don't understand why, in my case, common name is different from the target name of the scan. How these two domains are related(target domain and common name domain)? and how are releted common name and alternative name fields? In particular with DNS Alternative Name.
The target you scan is the name you have. This name gets translated to an IP address and this IP address then is used for the connection in nmap. But, an IP address can actually be resolved from many DNS names.
The names returned by nmap are the ones which the server returns inside the server certificate of the TLS connection. While there might be overlap with the name you give it does not need to be. Such differences occur for example if multiple DNS names point to the same IP address (and you have just chosen one of these) or if the server is configured in a way you did not expect. For example the certificate might return names which resolve to a totally different IP address in case the service is not intended to be reached directly but should only be reachable by a CDN or load balancer.