Question

What is resistance, and how does it work?

Answer 1

electrical resistance, you mean.

Ohm's law, from experiment, is resistance R = V/I, voltage / current.

an electric current involves the physical movement of electrons within the conductor. these electrons typically begin life as valence electrons -- in the outermost shell (valence band) of the, say, Copper atom. the application of the electric field is enough to rip these out and get them physically moving (drifting) through the wire.

but they will collide with the ions within the conductor. the resultant vibration of the ions we perceive as heat.

with insulators, the energy levels required to move valence electrons into the actual conduction band is much higher. insulators will "resist" the flow of electricity more.

alloys make for good heating elements because they have pure metals with loose valence electrons but also other metals that will impede their flow, increasing the heat output.