Brownian motion in many cases; they just bounce around randomly until Slot A happens to hit Tab B, as it were. The interplay of electromagnetic fields is often involved as well. Plus, there’s a fair amount of the molecular sized version of springs, levels, and so forth. They don’t need “free will” to work any more than a car engine does.
The laws of physics. What “tells” a rock to fall when you drop it ?
Not at all. We know enough about the machinery behind thoughts and emotions to know that molecules have no such things.
Some people (who are wrong ) think it is the power to act in a way that is completely indeterministic, a way that is not determined by heredity, environment, and prior influences. Other people (compatibilists) think that it is a matter of your action being caused in the right way by your desires (‘in the right way’ ruling out actions caused by coercion, or by desires which are the result of brainwashing, etc… Details differ widely among various compatibilists.)
They want various things. Electrons want protons, for example. If you like, subatomic particles are nothing but “want”. Their wants are all powerful, always clear, always constant.
A more useful question would be for subatomic particles to ask, what do humans want? Now, that’s a question endlessly confusing and yet seemingly of vast importance.
Amusingly, subatomic particles have no motivation to ask.