Quickly read Aquinas’ proof of the existence of God. Then read Sartre’s “Existentialism is a Humanism,” taking the time to take notes on the major elements of the each paragraph (a separate page in a notebook might come in handy). As you’re reading, keep in mind a couple things: We’ve been talking about the Truth and essence of something existing inside and existing internally. Often, this comes from a belief in the soul or God, and so it is tied to the religious intentions and ideals. Sartre’s existentialist philosophy starts from the premise that God does not exist, and therefore man must determine his own value and purpose, his own essence. In a God-less world, man exists before he determines his essence, and this is the essential step that guides the philosophy.
Give it your best shot and remember that “existence precedes essence.”