The island of Hawai'i comprises over half of the area of the state of Hawaii in the United States of America. To avoid confusion with the state, it is almost universally called the Big Island. It is home to the most active volcano in the world, located in Hawaii Volcanoes National Park, as well as the largest mountain in the world in volume (Mauna Loa) and the tallest mountain in the world as measured from its base on the sea floor to its peak (Mauna Kea).
There are two major airports if you are flying into the Big Island, Kona International Airport and Hilo International Airport. There are a few direct flights from the mainland, mostly from California and Seattle, but it is more common to arrive via Honolulu or Kahului. You should try to get a flight direct from the mainland to Kona to save time waiting (and walking) around the Honolulu airport. There are no direct flights to Hilo from the mainland.