Short answers, pulled from the story.
The Wehrmacht was the unified armed forces of Nazi Germany, comprising the Heer (army), Kriegsmarine (navy), and Luftwaffe (air force). It was officially created on the 21st of May 1935, when the Reichswehr was renamed and conscription was reintroduced in open defiance of the Treaty of Versailles.
About 18 million men served in the Wehrmacht over its existence from 1935 to 1945. Between 1935 and 1939 alone, 1.3 million were drafted and 2.4 million volunteered.
The clean Wehrmacht myth was the post-war claim by former officers, veterans' groups, and far-right authors that the Wehrmacht was an apolitical fighting force largely innocent of Nazi war crimes. Holocaust historian Omer Bartov wrote in 2003 that this was untrue and that the Wehrmacht was a willing instrument of genocide.
The Wehrmacht committed war crimes including massacres of civilians, cooperation with SS Einsatzgruppen death squads, deliberate starvation of Soviet civilians under the Hunger Plan, and the killing of Soviet prisoners of war. Between the launch of Operation Barbarossa and the following spring, 2.8 million of the 3.2 million Soviet prisoners taken died in German hands. Thomas Kuhne estimated 300,000 to 500,000 people were killed during Wehrmacht security warfare in the Soviet Union.
Blitzkrieg, meaning lightning war, was a combined-arms tactic that used light tanks, close air support, and motorized infantry to break through enemy lines, isolate formations, and collapse resistance quickly. The Wehrmacht employed it to devastating effect in Poland in 1939, France in 1940, and the early stages of the invasion of the Soviet Union in 1941. The Soviet forces studied the tactic and turned it against the retreating Wehrmacht from 1943 onward.
The Wehrmacht was officially dissolved by Allied Control Council Law 34 on the 20th of August 1946, which declared the OKW, OKH, the Ministry of Aviation, and the OKM disbanded, liquidated, and illegal. The last Wehrmacht unit had surrendered on the 4th of September 1945, when an isolated weather station in Svalbard yielded to a Norwegian relief ship.