Fig 8A transistor as a switchturn up the gateoff: no channel
A MOSFET, the transistor in every chip, has two n-type regions, the source and drain, in a block of p-type silicon. With no voltage on the gate there's no path between them, because the p-type silicon in between has no free electrons. A positive voltage on the gate, insulated from the silicon by a thin oxide layer, pulls electrons up to just under it. Above about 1.5 V here there are enough of them to form a thin channel that joins source to drain, and current flows. The gate draws no current, so a tiny voltage switches a much larger current on and off.