There were two bombs that were detonated. "Little Boy"  was detonated on Hiroshima, and "Fat Man" was used on Nagasaki.  ( Analt, Lindsey)
There was a secret organization that developed the bomb. It was called the Manhattan project. It was a secret group that created the atomic bomb.   there were labs that were placed all over the Untied States including Washington. Many of these labs were underground  and located on the east coast.  This was named rhe Manhattan project as a cover up  for the name of the actual protect. 
This was run by Dr. Robert Oppenheimer who fled from the  was a German jew ho fled from the Nazi's. (Analt, Lindsey)
There were three bombs that were created from the Manhattan project. The first atomic bomb test was codenamed " Trinity" and it was tested in Los Alamos on July 6th 1945.(Analt, Lindsey)
Soon after the test bomb worked, the first atomic bomb was dropped on Hiroshima on August 6, 1945 and the second bomb was dropped August 9, 1945.

"We knew the world would not be the same. A few people laughed, a few people cried, most people were silent. I remembered the line from the Hindu scripture, the Bhagavad-Gita. Vishnu is trying to persuade the Prince that he should do his duty and to impress him takes on his multi-armed form and says, "Now, I am become Death, the destroyer of worlds." I suppose we all felt that one way or another. "
J. Robert Oppenheimer” – director of Los Alamos  quote taken after the test.

Albert Einstein wrote a letter to the curent president  at the time Frankiln Roosevelt, to endorse the iea of  having a secret project working with nuclear weapon.(Analt,Lindsey)

 The pilot of the bomb flew into japn on a B-29 bomber called the  " Enola Gay".  The time of the bomb was dropped at 8:16, and three das later the bomb on Nagasaki took place. 
Before the bomb was detonated  America gave Japan an opprutinity to surrender. This was known as the Postdam Declaration, that said if japan doesn't surrender they would destroy Japan.