Quantity Discounts would create more discounts with more quantity.
This will help your customers to buy more quantity to get more discount.
Let's understand this by an example:
1 perfume cost $25 USD
2 perfumes cost for $40 USD
4 perfumes cost for $80 USD
When users will see this offer on the product page they would consider buying 2 perfumes as they are saving $10 and get more stocks in advance.
Basic steps to enable the app.
Hit the "Save & Publish" button.
Your campaign is all good to go now.