Glue a magnet to an axle.
Turn the axle to create spin. The spinning magnet creates a magnetic field. You are using kinetic energy to spin the magnet which can be converted into electrical energy. The first law of thermodynamics reveals that energy (matter) cannot be created or destroyed (only converted). Whatever energy is created in your spinning magnetic field will be equal or less than the electrical energy produced by its spin.
Induce an electric current by wrapping a length of wire around the magnet, but not attached to it. The wire should create a stationary loop around the magnet rotating in its center. The more you wrap the wire around the magnet, the more current is induced when you give the wire and magnet a spin. Verify by measuring the current with an ammeter. The ammeter measures current by touching its leads to either side of the wire.