Existentialism

I have met "existentilism" any one help me to understand what iS it???

Hello Imy and everyone,
I could select the following excerpts from different sources. I hope you'll find them useful, and I'm sorry if not!

Existentisalism is a "philosophical movement oriented toward two major themes, the analysis of human existance and the centrality of human choice. Existentialism’s chief theoretical energies are thus devoted to questions about ontology and decision. It traces its roots to the writings of Soren Kierkegaard and Freidrich Nietzsche. As a philosophy of human existence, existentialism found best 20th-century exponent in Karl Jaspers; as philosophy of human decision, its foremost representative was Jean-Paul Sartre...". Britannica Concise Encyclopedia

"...The classic text of French Existentialism is Sartre's Being and Nothingness, but many of its themes are anticipated in his novel Nausea. The ‘nausea’ refers to the feeling of disgust induced in the narrator by the sight of a chestnut tree in a park: the tree reveals the stark physicality of the meaninglessness of existence by simply being there. At the same time, it reveals the fundamental difference between the being of things and the being of human beings. Whilst the chestnut tree is always identical to itself and exists solely in-itself, human beings exist both in themselves and for themesleves. Because they exist for themselves and project themselves into a future existence by negating (nihilitating) what they are, human beings are free or, rather, condemned to freedom. The major ethical theses of Sartrean existentialism stem from the in-itself/for-itself distinction and from the insistence on human freedom. Freedom means that individuals have no destiny, and are obliged to choose freely what they become. The refuse to choose is in itself a choice, but it implies the self-deception of bad faith, or to surrender to the temptation to exist in the in-itself mode of natural object". From the Penguin Dictionary of Critical Theory

To understand this let's have a look at this explanation taken from the net:
The main idea (in Existentialism) is to distinguish the kind of being possessed by humans -- called être-pour-soi (Sartre) - from that possessed by ordinary objects (être--en-soi for Sartre).
The former, which is partly an actual condition of humans and partly something to be pursued, is essentially open-ended and free from determination by any already existing essence: 'existence precedes essence'. Hence the emphasis on freedom, choice and responsibility, evasion of which by relapsing into a 'thing-like' state (or trying to do so) is Sartrean 'bad faith'. Consciousness of this total open-endedness leads to dread (despair, anguish)

May Allah help you!

THANKS EZINMA FOR YOUR HELP.THANKS A LOT IN FACT I HAVE A PROBLEM WITH THIS MOVEMENTS I CONFUSE BETWEEN THEM.