The word switch has two major meanings:

1. To change from one thing to another. When you switch seats with your friend at lunch, you trade places. A baseball player might switch from batting right-handed to left-handed depending on the pitcher. Your family might switch from one internet provider to another, or you might switch the channel on TV. The key idea is making an exchange or change: you stop using or doing one thing and start using or doing something else instead.
2. A device that controls the flow of electricity. When you flip a light switch, you complete or break an electrical circuit, turning the lights on or off. Modern switches are usually small plastic toggles or buttons on the wall, but the first electrical switches were large levers that made a loud click when operated. Homes have dozens of switches controlling lights, fans, and appliances.