I couldn't quickly find a duplicate, but I wanted to address what Genki had to say (my emphasis):
It's very easy to form questions in Japanese. Basically, all you need to do is add ka at the end of a statement.
(I am) an international student.
Ryuugakusee desu ka.
(Are you) an international student?
It goes on to point out that this was a "yes/no" question. In other words, you can take a basic statement (that would be the answer to a yes/no question) and turn it into a question by adding か at the end.
It then follows with
Question sentences may also contain a "question word" like nan (what). In this lesson, we learn how to ask, and answer, questions using the following question words: nanji (what time), nansai (how old), nannensee (what year in school).
Senkoo wa nan desu ka
What is your major?
(Senkoo wa) eego desu.
(My major) is English.
In other words, when you want to ask WH-question like what?, you use a question word like the above. Notice that the first question was not a WH-question. So a WH-word was not used.
For context, you will later learn to drop certain words in casual speech, like です and か in questions.