The two coils are not wired to each other. Only the magnetic field in the iron core links them.
A control transformer like this one turns 120 volts into 24 volts for thermostats, doorbells, and contactor coils. The transformer on a utility pole works the same way at much higher voltage.
The picture shows a perfect transformer. A real one loses a little power as heat in its wire and core, so power out is nearly power in.
With no lamps on, a real transformer still draws a small current to keep the field going. The picture shows zero.
A real transformer has hundreds of turns. The picture draws fewer turns but keeps the same ratio. A real transformer is built for one ratio. The picture shows a different transformer and lamps for each ratio.
Each ratio uses lamps made for its secondary voltage. Every lamp is 24 W.
The readouts show what a meter would read. On AC that is the RMS value. It is the DC voltage that would light the lamp to the same brightness. The graph shows the voltage at each instant.
Amber dots show which way current flows and how much. They do not show electron speed. Real electrons drift less than a millimeter a second.
The dots move in the standard direction for drawing current. Electrons move the other way.
The purple arrows show the direction of the magnetic field. Brighter means a stronger field.
The field follows the primary voltage, not the lamp current. It still grows and shrinks with the lamps off.
On DC the field builds up once and then stops changing. The picture draws that first pulse as lasting a few thousandths of a second. The real length depends on the transformer. The arrows then stay at full strength because the iron core fills up with field.
On DC only the thin coil wire limits the primary current. The current gets far too high and the coil overheats. The picture does not put a number on it, and shows its direction with arrows only.
The battery bank is ten 12 V batteries in a row. It is a teaching setup. Never put DC on a transformer.
120 V is a nominal system voltage listed in 120.5(A). A real receptacle reads a little above or below 120.
The cord's green wire grounds the metal frame. Whether one secondary wire gets tied to ground is a separate lesson.