How do you splice a light fixture into an existing circuit at the box so that it turns off and on from a wall switch when there are three conduits of Wh Bl Gr wire 1 from main 1 from switch and 1?

To splice a light fixture into an existing circuit with three conduits containing white (neutral), black (hot), and green (ground) wires, first, turn off the power at the circuit breaker. Connect the black wire from the switch to the black wire of the fixture; this will allow the switch to control the light. Connect the white wires (from the main, switch, and fixture) together as they serve as the neutral connection, and connect all green wires together for grounding. Finally, ensure all connections are secure and properly insulated before restoring power.