B Which component of light is a photon?

What does that mean, that the photon is just a probability wave until it interacts with something?

 

Not a 'probability wave', just fluctuations (waves) in an electromagnetic field.
'Interacting with something' generally means that the something has absorbed some energy of the wave.
This results in some electrons gaining energy, however electrons can only transition to a more excited state in discrete steps, (quanta).
The number of such steps occurring is countable by an appropriate measuring device, so from that perspective light is behaving more like a bunch of particles than a continuous wave.

 

And to extend this just a bit for the OP, what's also true is that not just any "photon" can excite just any electron. That ability depends on the frequency of the wave that causes the excitation so details of the "photon nature" side of a beam of light is a directly affected by the frequency of the light wave.

Photons are not "particles" in the classical view of particles, they are instead more accurately referred to as "quantum particles" or better still, "quantum objects".

 

The same as when you throw a dice. You know a side will come come up with a probability of 1/6 but nothing happens until you throw the dice.

QM is a theory about observations that appear here in a common sense classical world. We can predict probabilities of those observations but nothing happens until an observation actually occurs.

With light we can predict the probabilities of observing a photon, and that is done with the wave-function (also called a probability wave) but nothing happens until it is actually observed.

Note: What I said above isnt quite true because photons don't really have a wave-function in a usual sense. But liberties with the truth about photons is often taken in beginner texts.

Thanks
Bill