It is most common to use the end particle ka when making a question sentence. Simply add ka to the end of a statement.
りゅがくせいですか。 (Are you) an international student?
ryuugakusee desu ka.
Questions may also contain question words such as nan (what), nanji (what time), nansai (how old), nannensee (what year in school).
いまなんじですか。 What time is it now?
ima nanji desu ka.
メアリさんはなんさいですか。 How old are you, Mary?
Mearii san wa nansai desu ka.