1. Conductive tape (you can find it here). This tape has the peculiarity of having steel fibers mixed with polyester fibers.
3. A low power electric/electronic circuit you want to turn on and off
Connect one end of the first piece of tape to a power generator or battery, 5V is enough. Connect one end of the other piece of tape to the other pole of the battery/generator i.e. via an LED. See picture.
Be sure you connected the LED with the right polarity.
PLEASE NOTE: this is a switch for low currents and low voltages only!