Ignition issues can be a real pain to both diagnose and deal with. Sure, generally speaking, having a faulty ignition coil is a better problem to have than a worn-out turbo or clogged DPF, but ...
A windings road:It all starts with the concepts of inductance and electromagnetism. Inside an ignition coil there are two sets of wire windings (aka coils, that's why it's called a "coil," get it?).