The answer to 'how to install light fixture' is to first turn off the power to the fixture at the circuit breaker. Then, remove the old light fixture by unscrewing it from the electrical box and disconnecting the wires. Next, attach the new light fixture's mounting bracket to the electrical box, connect the wires (black to black, white to white, and ground to ground), and secure the fixture to the mounting bracket. Finally, restore power to the circuit and test the new light fixture.
It's important to follow all safety precautions, including turning off power, using insulated tools, and ensuring proper wiring connections. If you're not comfortable working with electricity, it's best to hire a licensed electrician to handle the installation.