World War Two in Europe began on 3rd September 1939, when the Prime Minister of Britain, Neville Chamberlain, declared war on Germany. It involved many of the world's countries. It started because Germany invaded Poland.
The Second World War was started by Germany in an unprovoked attack on Poland. Britain and France declared war on Germany after Hitler had refused to abort his invasion of Poland.
World War 2 ended with the unconditional surrender of the Axis powers in 1945 in May.
The First World War had to be fought mainly on the ground. World War Two was a different kind of war as it was both on the ground and from the air.