What is the benefit of getting some answers back under a DNS message, and how can you know that there are several such answers?

edit

Not sure I understand the question here, but lets see.

"What is the benefit of getting some answers back under a DNS message"

Well, the immediate benefit is that you get answers to the questions you asked the DNS server. That sounds obvious to me. If by "some answers" you mean "multiple answers" then the question makes more sense to me. The thing is that the query, as it's called in DNS, can have multiple answers related to it.

"And how can you know there are several such answers"

In the response message, as it's called in DNS, there is a field called "Answer RRs", which stands for Resource Records. This lists the number of answers in the response message.

"Why DNS answer called Request Response"

If you look carefully it's not called that. If you refer to the complete message, it's a response to a standard query. That is because the DNS protocol has other types of interactions, between clients and servers, and between multiple servers.