The first obvious component of this smartphone/tablet hybrid is the stylus. According to Samsung Tomorrow, the S Pen "uses electromagnetic induction technology and has pressure sensitivity equal to a regular pen." This also means that the harder you write, the darker the stylus can draw. Altogether, the pen can sense 256 different levels of hardness.
The third layer is the digitizer, which interacts with the stylus and establishes an electronic magnetic field to block "the noise and magnetism through the shield plate." The digitizer also senses where the stylus and/or your finger are, and how hard they're being pressed against the screen.
I would have liked it if this piece went into more detail about where exactly everything is on the main PC board, however. Mainly because I'm curious about where this gyro sensor and light sensor are that they speak of.
Still, if you want to see more of the Galaxy Note's insides, hit the link above and explore away.