Fertilizer is kind of strange stuff. It gives the seeds good stuff to munch on while they are growing, so it is a useful thing as well. All the little parts are something different for the plant. One is nitrogen, one is calcium, one is phosphorous, one is potassium (I think), and I am pretty sure there are more, but I don’t actually know them. There are different formulas, too, depending on what works best with your soil.
I find it interesting that all these little particles have their own unique shape, and colour, making each blend of fertilizer a different mix of white and black. I suppose the plants don’t care what shape and colour the particles are, so long as they have free access to them as long as they need them. (But not too much access or else they get fertilizer burn – kind of like overeating makes you feel ill)