ok. existentialism is the ideology that arose during the 20th century that infers that the life of an individual is completely purposeless and meaningless, and anything that we want done about this has to be done by OURSELVES.
without religion [existentialists are commonly associated with atheism] a person is not born with something BIG to do in life, and there are just so many people in the world that if you don't do anything, nothing really happens, and you are simply WAITING AROUND TO DIE, to put it crudely.
this view of the world arose in the beginning of the 20th century [or late 19th] with the 'discoveries' made by Charles Darwin concerning natural selection and the theory of evolution. this was a massive kick in the guts to the religious world, who believed that humans came from adam and eve. events throughout the rest of the 20th century emphasised the insignificance of human life even further, with the holocaust, and the bombing of hiroshima, etc.
i have not STUDIED the hours, but i have seen it, and i know that virginia woolfe lived during this era of realisation [not sure if its actually called the era of realisation, it just suits the idea i'm putting across], and that the reason for her suicide was justified on the hoplessness she felt due to the existentialist nature of this new world
(and particularly the events of the holocaust)
yeh i watched the extras on the DVD, its really interesting. did you like it?
i hope that kinda explains it for ya, i dunno if i'm being too vague.