Existentialism is "a philosophical theory or approach which emphasizes the existence of the individual person as a free and responsible agent determining their own development through acts of the will.... Existentialism emphasizes action, freedom, and decision... individuality, consciousness, ... choice, and responsibility... as fundamental to human existence.... Existence precedes essence for human beings.... Objects always have a definite purpose and this purpose is known prior to the creation of the object. On the other hand, humans are not born with a definite purpose." (Google search)
Existentialists proactively aim to be wide awake individuated persons, not to passively acquiesce or emulatively woke to be herd animals. (I was going to say "copycat" but cats don't copy, so that word implies an improper association. "Herding cats" is notoriously difficult.) An exitentialist asserts to consciously live his (her, other) own life, not just buzzingly serve like a bee in its hive: a wokie or a MAGA or other "conformist".
Existentialists are famously "alienated": isolated and estranged; they never alienate themselves: transfer ownership of (property rights) to their soul another person or group. An existentialist endeavors to figure out life for himself, not buy what somebody else such as a rebbe or other pied piper tells him it is. Like Odysseus, he refuses to be seduced by the songs of Sirens (Muzak?). Better Sisyphus than a 2-legged sheep (see picture above).
I (BMcC[18-11-46-503]) am an existentialist: My life matters to me, not any set, the idea of which I might be a member, e.g.: "Black lives matter", or "white lives matter" or #MeToo (U-2 aka: "Dragon lady"?) or whatever.
Only individuals exist, or can matter to me, for better or for worse, and all groups are bad, albeit some groups are badder than others. A mob of Trumpies or sports fans or hassids is even worse than the audience of a classical music symphony performance. But none is good. I like "social distancing" – 612 feet, please. If you were socially conditioned to be offended by "body odor" and you are offended by me, you are too close. Etcetera.
"Existentialism" is a misnomer: Existentialism is the: un-ism, the: not-any-ism. An existentialist does not follow anybody, including any Southern baptist preacher pied piper who says he's been to some mountaintop and seen the promised land. I've been to my mountain top, and I've seen the promised land. It's the light at the end of the tunnel. It's a Vietcong with a flashlight. No way, Jose.
What should a leader do, existentially? He (she, other) should tell his would-be followers to follow his example, not his scent trail (his "beliefs"), and follow nobody but rather, like himself, creatively take responsibility for shaping each his own life: "Shoo! Get on with it, and maybe some day we will meet again as peers."
The only value is in my living acts of valuing. Is does not imply ought. Nothing which exists has any intrinsic value; it just may (or may not) be useful for my present and/or future purpose(s). For instance, the Judeo-Curistian Bible has a lot of great stuff in it – just don't believe a word it says, like you probably don't believe in Zeus, or in Wotan. One Item: Patriarch Abraham is a great example of a person who, like Adolf Eichmann, just followed orders. "Another:" The Abrahamic Deity is a criminal for having ordered Abraham to murder his son, and for having conducted an unethical medical experiment on righteous man Job. See how much fun people's beliefs can be if you are not a believer?
For an existentialist, thereis at least life after birth. Is there also life after death? (Click here for Hieronymus Bosch's opinion)