In order to generate electricity using gravity force you must find a source where gravity causes movement. Movement is kinetic energy, and you need to convert that into electricity. A stream that flows downhill, a waterfall, rain pouring out of a downspout — all of these are considered movement caused by gravity. You need to therefore find an appropriate location.
The next step is to install a turbine. These machines work similarly to a water wheel. One part of the electric turbine is spun by a force, in this case liquid being pulled by gravity. The turning of the wheel spins a central shaft, which in turn will rotate a magnet surrounded by copper wire. This creates an electrical current, which can then be used immediately or stored in a battery.
The final step is to use the electricity produced. As mentioned above, the bigger the source the more electricity you can produce. But keep in mind that the bigger the source, the bigger the turbine you’ll need to handle it.