The answer to 'how to install light fixture' is to first turn off the power to the light fixture at the circuit breaker or light switch. Then, remove the existing light fixture by unscrewing it from the electrical box. Connect the new fixture's wires to the corresponding wires in the electrical box, matching the colors (black to black, white to white, and green or bare copper to the green or bare copper ground wire). Secure the fixture to the electrical box and install any decorative components. Finally, turn the power back on and test the new light fixture.
It's important to follow all safety precautions when working with electricity, including turning off power, using insulated tools, and not touching live wires. If you're not comfortable performing electrical work, it's best to hire a licensed electrician to ensure the job is done safely and up to code.