To start a price tier, edit your product from your store page:
Each tier has a minimum number purchased and a new unit price. 1 – lowest tier takes the price from the product. Each subsequent range is configured as the minimum quantity to the next lowest quantity. Make as many tiers as you need:
If you ever want to discontinue a price tier, you can delete it from the same page:
When you have set this all up, here is what buyers will see on the product page: