It is an important event during WW2 that liberated the north of 
Franceball from the hand of 
evils. So the american landing from air and Operation Tonga (a part of D Day) happened before the allies landed at their specific beach(es) which was Utah and Omaha beach for the American troops, Gold and Sword beach for the British troops and Juno beach for the Canadian troops.
So basically after freeing the lower of the clays of one of the axis leader countries (who had a sudden personality change, split into Fascist Italy occupated by the Nazi and Antifascist Italy occupied by the Americans), the allies-of-the-west want to free this poor ally who got wrecked by this nazi guy at the start France and they planned to land some troops on the beaches of Normandy and they even had did practice before they start the operation. So at midnight the mighty English union USAball, UKball, Canadaball, and some resistance just land some troops on the clay of Normandyball (Operation Tonga, a part of it) and at 6:30 a.m. 6 June 1944, allied infantry and armored divisions began landing on the coast of France. The target 50-mile (80 km) stretch of the Normandy coast was divided into five sectors: Utah, Omaha, Gold, Juno, and Sword. Strong winds blew the landing craft east of their intended positions, particularly at Utah and Omaha. The men landed under heavy fire from gun emplacements overlooking the beaches, and the shore was mined and covered with obstacles such as wooden stakes, metal tripods, and barbed wire, making the work of the beach-clearing teams difficult and dangerous. Casualties were heaviest at Omaha, with its high cliffs. At Gold, Juno, and Sword, several fortified towns were cleared in house-to-house fighting, and two major gun emplacements at Gold were disabled using specialized tanks.
The Allies failed to achieve any of their goals on the first day. Carentan, Saint-Lô, and Bayeux remained in German hands, and Caen, a major objective, was not captured until 21 July. Only two of the beaches (Juno and Gold) were linked on the first day, and all five beachheads were not connected until 12 June; however, the operation gained a foothold that the Allies gradually expanded over the coming months. German casualties on D-Day have been estimated at 4,000 to 9,000 men. Allied casualties were documented for at least 10,000, with 4,414 confirmed dead.