According to the terms of the Versailles Treaty at the end of the First World War, Germany's military was limited to a force so tiny as to be utterly irrelevant in any major conflicts. When Hitler came to power, he began to rebuild the military in secret, in direct contravention of the Treaty.
When and how did the larger portion of the German population learn that their country had a massive, well equipped, and powerful military again?
Hitler's saber rattling and belligerence in the years leading up to the war terrified many of his citizens, to say nothing of his potential adversaries, but this would likely have been true regardless of whether or not the full scale of the rearmament was public knowledge. I imagine that, some time around the invasion of Poland, Hitler must have revealed his achievements, whether the revelation was intended to intimidate his enemies or reassure his subjects.