The bombing of Hiroshima took place on August 6, 1945.  It all started when the Enola Gay, a B-29 bomber took off and headed northwest for Japan coming from the Island of Tinian.  Hiroshima was the main place that the bomber was heading.  The pilot of the bomber was Colonel Paul Tibbits who was the commander of the 509th Composite Group.  He flew the bomber very low and then gradually got higher.  At that moment they dropped the bomb named "Little Boy".  "Little Boy" was a uranium bomb that weighed 9,700 pounds and was dropped over the city.  Once the bomb hit the Enola Gay was already 11 1/2 miles away but it still shook from the bomb.  The men in the bomber plane looked back on Hiroshima and Tibbits said, "The City was hidden by that awful cloud....boiling up, mushrooming, terrible and incredibly tall".  

On the morning that this happened before the bombing it was a calm and sunny morning.  By 8:15, when the attack happened the city was no longer calm.  Soldiers, men, women, children, everyone who could were outside clearing firebreaks.  Any flammable material within 6,400 feet burst into flames immediately.  Even birds were ignited into flames while flying in mid-air.  People who were in their homes were even hurt.  They were severely wounded by glass flying through their windows and one boy was even blown out of a window in his house by the intense explosion.  

Nearly everyone in the whole city experienced this.  Even people who weren't in the worst part of it still experienced severe heat and the deafening boom.  Within a one mile circumference all of the buildings were completely destroyed and within a three mile circumference every building was damaged.  There is no definite amount of people who died from this but they think that there were probably around 70,000 people who were killed from the initial part of it and after the long term effects there were about 200,000 deaths. 

http://www.cfo.doe.gov/me70/manhattan/hiroshima.htm