いまなんじですか。 (ima nanji desu ka)
What time is it now?
In this sentence, いま (今) means "now," なん (何) means "what," and じ(時) means "hour." Literally, you're asking what hour it is.
To answer this question, you simply say what hour it is, followed by じ. If it is 5 o'clock, you say 五時です (ごじです = goji desu). To specify if it is AM (ごぜん = gozen) or PM (ごご = gogo), you just place it before the time.
ごぜんろくじです。 (gozen rokuji desu)
It is 6 o'clock AM.
ごごななじです。 (gogo nanaji desu)
It is 7 o'clock PM.
How about if you want to say 7:30 or a specific minute? Well, it gets a little more complicated, so I'll explain it in the next lesson.