All of them are the result of “quanta” of force interacting. To understand force, we must anthropomorphise it: ascribe an inner will to it.
Action is always reaction, yes. The will to power is a pathos, i.e., something that is aroused.
“The question is ultimately whether we really recognize the will as efficient, whether we believe in the causality of the will: if we do—and at bottom our faith in this is nothing less than our faith in causality itself—, then we must perform the experiment of positing the causality of the will hypothetically as the only one.”
[Nietzsche, Beyond Good and Evil, section 36.]
Causality - the idea of cause and effect - is a simplification of the flux of Becoming. In order to be conscious of anything at all, we have to simplify it. Note that “simple” etymologically means “single”: we have to discern “entities” (units or unities) within the flux, which are really only relatively different and separate. This is what logic is. Logic simplifies Becoming to interactions of “Beings” (entities). Nietzsche’s insight is that we can only explain (rather than merely describe, i.e., model) these interactions by conceiving these Beings as having a “will”: we say this Being behaves such and such because it wants to do this or that. We can understand this - empathise with this - because we humans know what it is to will: will is what is immediately intelligible to us, because we “know” it firsthand - feel it. We cannot explain this feeling; it’s just there. We can understand that it is aroused by something - by an image, an image of Being, toward which we then want to become -, but we cannot explain the nature of this pathos by any other, “deeper” analogy.
There is no such end in nature, but there is the illusion of such ends. The will is aroused by an image (German Vorstellung) - an image of “Being” (in the Parmenidean sense): an image of perfection, absoluteness - an ideal.
Eternal Recurrence means Becoming forms a great ring of Being (in a higher dimension). So Becoming does not become Being, but Being - the Ring of Recurrence - consists of Becoming.
Becoming, however, can only be understood as the result of the will to Being (the will aroused by an image of “Being”, which then strives to realise this image).
As I said, Nietzsche says the highest will to power is to stamp Becoming with the character of Being. This means will to power is always a will to approximate Becoming to Being - for instance, by simplification. So the simplification of the flux of Becoming into entities which affect each other must already be understood as an effect of the will to power. And this presupposes the existence of relative entities; the simplification consists in falsifying these as “absolute” (thus the idea of absolute duration and unity - “Being” in the Parmenidean sense - is a simplification of the actual occurrence of relative duration and unity).