Explain the basic arguments of Sartrean existentialism

What will be an ideal response?

Existentialism examined the unique nature of individual experience within an indifferent universe. Focusing on matters of human freedom, choice, and responsibility, it rose to prominence through the efforts of the French left-wing intellectual Jean-Paul Sartre. Sartre's philosophy took as its premise the idea that existence precedes essence, that is, that one's material being exists prior to and independent of any intrinsic factors. Philosophers from Descartes through Kant followed the ancients by defending the notion that primary internal principles of being preceded being itself—a view that was metaphysically compatible with Christian theology. Sartre's premise challenged the fundamentals of this traditional philosophy.
Sartre offered that there is no preexisting blueprint for human beings, no fixed essence or nature. We are not imbued with any special divinity, nor are we (by nature) rational. We are neither imprisoned by unconscious forces (as Freud had held) nor determined by specific economic conditions (as Marx had maintained). Born into the world as body/matter, we proceed to make the choices by which we form our own natures. In Sartre's analysis, each individual is the sum of his or her actions; "We are what we choose to be," he insisted. According to Sartre, without a religious or spiritual framework, the human condition is one of anxiety experienced in the face of nothingness and the inevitability of death. Such anxiety is compounded because we alone are responsible for our actions.