That’s like asking what/how to paint if you happen to be holding a brush. The answer is: something/now.
Normative, for those who would otherwise study the brush, bristle by bristle, and forget to paint anything while there’s still time. Or stand around waiting for someone to tell them what to paint, or wait for an audience to paint for…thinking that without an audience, what’s the point? WHY should I paint THAT and for WHO?
How do you cash in this analogy, or how and why do you “paint” with an existentialist viewpoint? Exercise your freedom. Bind yourself to laws of your OWN making. How do you make laws? Find the natural laws within. At risk of sounding clumsy, I define it as those laws hidden in plain view in your deepest heart, woven into one’s being, that which hold literary or aesthetic value, thus yielding the highest lasting positive impact when adhered to. How did it get that way? Not relevant, although it could all be Darwinian. Point is, you get to decide what has meaning, but not totally, most of that is decided for you. You get to decide whether or not you are in touch with it. Like the quote in my signature says.
Socially, we should live assuming that others have the same freedoms, and we should integrate this knowledge into our own set of laws and behaviors, to further define our laws.
In regard to logic, I see it as similar to Des Cartes. You start with the axiom “there exists” and move outward geometrically*, empirically & rationally, until you conclude, quite logically, that you are an existentialist, and that you know, more or less, how you might as well live.
Existentialism is more of a playing field itself, and the strategies on the field, and the science of game, may be better served with a Spinozan point of view. In other words, other philosophies are still worthwhile, but Existentialism is the king daddy.
*don’t ask
One time on actor’s studio sean penn was asked his favorite word. He said: courage.
I thought: fuckin’ A.
Courage is flipping the bird at the heavens and the void inside you. We are free to rebel against the human condition. Courage is the way to do it. Courage under fire, courage unto death. Why is this a fuckin A moment for me? I don’t know. But it’s freeing as all hell and as pure as 2+2.