This Indian project helps to understand how it is possible to produce electricity from a magnet, a copper coil and a movement. The same principle is used in most electricity plants. Depending on the plant, the movement is produced by different means (for instance by transferring the strength of water or steam to turbines).
In the case of this DIYs project, the movement is produced by the pressure of the air. This pressure is transfered to a turbine. The turbine rotates an electric generator which supplies electricity to a LED light on top of the bottle.
Following the same concept, engineers are trying to produce electricity from the movements of waves or tides. These new sources of energy are renewable and do not produce any pollution. They could be an answer to some of our environmental issues.