The simplest igniter consists of a short wire with a high resistivity section in the center that is coated with some explosive. The igniter is inserted in the back of an engine and held in place with a plastic plug or with a small ball of recovery wadding held in with tape.
To launch the rocket, it is placed on the launch wire and the launch controller is attached to the igniter wires with two alligator clips. To fire the rocket, a current is pushed through the wire causing it to heat up and ignite the explosive. The explosive then ignites the engine. Note how the igniter wires are bent into an arc so that the alligator clips can get a better grip on it.
A different type of igniter is the copperhead. This igniter consists of a strip of plastic with copper on both sides. A small ball of conductive explosive is placed on one end. It is also inserted into an engine, but a special clip is used to attach it to the launch controller. The clip has two wires attached to the two sides of the clip. When the clip is placed on the end of the igniter, the two wires attach to the two copper films. The rocket is fired in the same way, with a current driven through the copper strips that ignites the explosive. We have had a lot of misfires using copperhead igniters. The problem is usually a short across the plastic strip caused by bending or twisting the igniter such that the two copper strips come into contact.
Igniterman style igniters are made by stripping the insulation off of a quarter inch of two wires and then twisting all but the end of the wires so that the stripped ends are close (about the thickness of a thick sheet of paper) but not touching. This end is then dipped in a flammable conductor that creates a thin film between the two wires. Running a current through the wires and the film causes the film to ignite. After the film dries, the igniter is dipped in a pyrogen mixture. This mixture causes a small explosion that ignites the rocket fuel.