Well, in my experience it's safest to have at least a little background knowledge on what caused the war. Know about the assassination of the Archduke as the last straw on the camel's back, and about the basic ideological lead ups. Just to simply summarise, you should know that the following had impacts on the world of the early 20th century:
Nationalism:
* The strong feeling of support for one’s country
* Nationalists believed the needs of their country were more important than the needs of other nations.
* Wanted their country to be richest and most important, and seen that way by others
* Nationalism often made people aggressive towards other nations, and unforgiving if they thought their country had been wronged
Imperialism:
* Desire of countries to own colonies and create an empire
* Countries often wanted the same area of land, which led to tension between them
* As each European nation gained colonies, these colonies became committed to helping the motherland in the event of a war
Militarism:
* Militarists believed their countries should be well armed, and military methods could be used to gain nationalist needs
* Great Powers competed in building up their armed forces and supply of weapons
* This became the Arms Race and added to fear and anger towards each other
Alliance System:
* Alliances are agreements between nations
* In the war, Europe was split into two armed camps, which became increasingly hostile towards one another
* Triple Alliance (Germany, Austria-Hungary, Italy)
* Triple Entente (Britain, France, Russia)
* Thus, a conflict between counties then included other countries as well