To switch means to substitute one item for another, and switch can also be used as a noun to refer to that substitution.
Ex: Before we head outside again, I want to switch shoes. It's supposed to rain and I don't want to get caught outside without my rainboots.
Ex: The switch from coal to solar or wind power may be expensive at first, but in the long run the sustainable energy source will prove to be more cost-effective.
The expression bait and switch refers to a deceptive sales technique in which a store lures in customers by offering a sale, but then tells the customers that the sale item is out of stock in order to sell a more expensive item. Another expression with switch is to switch gears, or sometimes to shift gears, which means that someone suddenly changes what they are doing or the way they feel about something.
Ex: Consumers need to watch out for bait and switch advertising at car dealerships. The dealer will advertise a low price for vehicles, but when you arrive to buy a car you'll find that they have sold all the affordable models and the only ones left will be out of your price range.