In the morning you could say Ohayo or Ohayo Gozaimasu.
However, you should not say Ohayo to anyone but friends or family. This is because Ohayo is informal and if you are speaking to your boss or someone else that is really important you should say Ohayo Gozaimasu because it is more formal.
You would pronounce it like Oh-high-yoh or Oh-high-yoh goh-za-ee-moss.
