Yom HaZikaron honors Israeli fallen soldiers and victims of terrorism. It is more somber than the American Memorial Day — when a commemorative siren blares at 8 pm and 11 am, the entire country of Israel (including highway traffic) comes to a standstill.
Yom HaZikaron and Yom HaAtzmaut are deliberately observed back-to-back, to recognize that Israel's continued existence is because of the soldiers and civilians who sacrificed their lives. It is customary to wear a white top and dark pants or skirt to a Yom HaZikaron ceremony.
Yom HaAtzmaut celebrates the formal establishment of the State of Israel in 1948 (that year, the 5th of Iyar corresponded to May 14). Celebrations include Israeli dancing, singing, and other joyous festivities (often outdoors).