What is the significance or result of the German invasion of Denmark and Norway?

Norway was an important source of iron ore,
but there were two more important reasons for the German invasion.  Primary was the
strategic location of the country, and if the British had seized Norway
Germany would have been outflanked to the north before the war was well underway.  This
not only would have been disastrous in terms of losing control of the northern seas and
the exit from the Baltic, but would have left the British in control of a direst route
to Finland and Russia.  The primary reason Hitler invaded Norway was to forestall this,
which was indeed the plan of the British.

Although those
two reasons were important, there was a third very important reason.  That was the
company Norsk Hydro, the world's only commercial source of deuterium,
known as "heavy water." This is essentially water with an extra hydrogen
atom, and which was used as the moderating agent to control the reaction of uranium in
atomic research.  The method of creating an atomic bomb which was being pursued by
German scientists depended on heavy water.

German, Russian
and British scientists had been working on an atomic bomb since before the First World
War.  Norsk Hydro's production was immensely increased during the war, but the shipment
of large quantities was stopped by various means.  There were several attempts at
sabotage, some successful, and one major commando raid on the plant.  It could not be
successfully destroyed by bombing because of its position inside a steep valley at the
base of a mountain.  In February of 1943 the facility was heavily though temporarily
damaged by a raid carried out by Norwegian and British commandos, some of whom had been
living on the snow covered mountains for months.  On 20 Feb., 1944, the Germans shipped
a large quantity of deuterium in barrels on a ferry down Lake Tinnsjo; the ferry was
sunk by a time bomb set by Knut Haukelid, a Norwegian commando.  This was essentially
the end of Germany's attempt to create an atomic bomb, although it was actually beyond
their capabilities.  They simply did not have the money or manpower available to carry
out the massive industrial effort required at the time.