Short answers, pulled from the story.
Major General Leslie Groves of the U.S. Army Corps of Engineers directed the Manhattan Project from 1942 to 1946, with headquarters in Washington, D.C. J. Robert Oppenheimer served as director of the Los Alamos Laboratory, where the weapons were designed. The project's name came from its first Army headquarters in Manhattan, at 270 Broadway in New York.
At its peak the Manhattan Project employed nearly 130,000 people. The total cost was nearly two billion U.S. dollars. Over 80 percent of that cost went toward building and operating the facilities that produced the fissile material, rather than the weapons themselves.
The three principal sites were the Clinton Engineer Works at Oak Ridge, Tennessee, where enriched uranium was produced; the Hanford Engineer Works near Richland, Washington, where plutonium was produced in the world's first industrial-scale nuclear reactors; and the Los Alamos Laboratory in New Mexico, where the weapons were designed. Dozens of supporting facilities operated across the United States, Canada, and the United Kingdom.
In April 1944, physicist Emilio Segrè discovered that plutonium produced in reactors contained a much higher concentration of plutonium-240 than cyclotron plutonium, causing up to five times the spontaneous fission rate. In a gun-type weapon this would trigger a premature chain reaction before the components could fully assemble, producing a fizzle rather than a full explosion. The project shifted entirely to the more complex implosion design as a result.
Trinity was the first detonation of a nuclear device in history. It took place on the 16th of July 1945 at White Sands Proving Ground in New Mexico. The device tested was an implosion-type plutonium bomb, the same design as Fat Man, which was later used at Nagasaki.
Britain contributed foundational research through the MAUD Committee and its earlier Tube Alloys program, which was more advanced than the American project in 1940 and 1941. A British Mission arrived at U.S. sites in December 1943 and included scientists such as Niels Bohr, Otto Frisch, Klaus Fuchs, and Rudolf Peierls. Groves later said there probably would have been no bomb dropped on Hiroshima without Britain's impetus, particularly Winston Churchill's. The Quebec Agreement of August 1943 formalized the joint effort and established that nuclear weapons could not be used against another country without the mutual consent of both nations.