Here's what's inside an ignition coil and how it works to increase the voltage to fire a spark on your car:

Here's a few photos of the ignition coil.

Starting with the coil, removed from my Toyota Corolla:

An ignition coil is located on top of an overhead cam engine. Its responsible for increasing voltage from the car's 12V to the thousands of volts needed to fire a spark in the combustion chamber:

When chopped open you can see the coil and other layers, along with the center iron core:

Here are all the components inside the ignition coil:

Here's a system diagram of how the ignition coil works electrically:

Note its the voltage spike caused by varying the electromagnetic field that fires the spark, and not just the step up transformer itself.