The instructions are fine. What's probably not making sense is that Poppers use 12 to 18 VDC fans that are in series with a drop down resistor. The project removes the drop down resistor, and uses a transformer to step down the voltage to the fan, so that it can be driven directly. The dimmer on the line side of the transformer allows the fan to be modulated. The AC/DC conversion is dine by four diodes soldered to the motor, so you don't have to worry about it.

Once this is doen, you can crank up the fan early, use a lot of beans with relatively cool air (more fan, less heat). Then as the beans lighten up, you turn down fan and increase the heat to finish the roast. In the 1980s, poppers were built like appliances, and lasted forever; but since then they have been reclassified as novelty items, and are designed for a few moths use. So keeping all these added controls external, and movable to the next popper, is well advised.