How did the Spanish Civil War contribute to the outbreak of World War 2?

It didn't. The Spanish civil war was between the republicans (communists in this case, heavily backed by Stalinist Russia) and the fascists (backed by Nazi Germany and Fascist Italy). It was long and bloody - like many civil wars. The country was a wreck by the time it ended. The Russian's stole what they could (mostly several museum collections which they still hold) and went home. The Germans tested their tactics and weapons and got their forces a little more ready for the real fight to come. Spain was such a wreck by the end of the war that they were unable to participate in WWII except on the far fringes (limited trade, fixing a U boat or two) for their ally Germany. Their nation took about twenty years to truly recover. None of this really mattered when it came to starting WWII, which was a titanic struggle between Nazi Germany and Communist Russia to see who would be able to balance the burgeoning power of the USA. All other WWII battles were peripheral to this struggle which ended with Germany out of the world power game for all time and Communist Russia the dominant power over about a third of the globe.