The way your in-cart discounts apply depends on the types of discounts you are using.
Automatic vs coupon discounts
Automatic discounts apply automatically at cart or checkout when customers add eligible items to their cart. They do not require any action from the customer.
Coupon discounts require customers to enter a discount code during the checkout process to receive the discount. Customers need to manually input the code to benefit from the discount.
Product vs order discounts
Product discounts apply directly to individual items in the cart. You can choose the products you want to make eligible for the discount.
Order discounts apply to the entire order after any product discounts and before taxes.
If those two types of discounts are set to combine, then first all the product discounts apply, and the order discount is applied next.
For example, if a product discount of 20% is applied to a product priced at $100, the discount is applied first, resulting in a subtotal of $80 for that product. If, after that, an order discount of $10 is also applied, the final total would be $70.