Defining a philosophical school and even philosophy as a whole is always hard, but here's a little attempt at some short talking points about existentialism.
No matter what we do, we're always making decisions about actions. Even the act of not acting is still an action and by this the existence of neutrality becomes difficult, if not impossible to defend in existentialism.
2. you ever wonder why we're here?
Existentialism's answer to that question is more or less that there doesn't have to be a set reason. For some, like Kierkegaard, creation by a god was perfectly reasonable, as well as what logically follows from that. This is not to say that's all there was to it for him, but it's just to show that it leaves room for some dogma, if it can be enforced at all. For others, it is more about the emotive creation of meaning in the human experience.
3. why? because. but why?
I've already used the word once, but dogma is something that existentialism chiefly questions. It is meant to challenge, bend, or even break dogma that cannot be enforced. For instance Jean-Paul Sartre openly challenged French colonial attitudes, even advocating violent revolt, despite being a French citizen. The dogma of French exceptionalism, for lack of a better term, was a major target of his, but even beyond that the role of humanity, which brings us full circle, in that there is a lot of responsibility that comes with existing.
Trying to make sense of this apparently senseless life. We over analyze and take ownership in our stance in order to compensate for its elusiveness. Perhaps there is no better sense to anything than senselessness because in this senselessness there is wonder entertainment and we are almost certainty wrong or incomplete in our understanding.
Christianity’s methods of understanding life lacks an attempt to explain the true nature of the universe, what the self is and what the meaning of life is and how to deal with it all. Instead it studies and maintains history with an authoritative figure looking over everything.
One of the possible risks is that sin or being a bad person defines your next reality, as a sense of judgement.
This combined with the risk of Permadeath to me means the meaning of life is to live it with good, trying not to die.
And luckily enough this path is also one of love, sustainability, high purpose, respect and the endgame should be a blast for awhile