To apply a discount on the cart, you must create at least one Cart discount rule.
Go to YITH Plugins > Dynamic Pricing and Discounts > Cart Discount, click on Add new, give a name to the new rule and proceed with the configuration of the other parameters.
There is no limit to the number of rules you can create.
If the cart satisfies the conditions of different discount rules, they will apply according to the priority you specify in the rule settings next to Priority. In the above image, for example, the rule has a 2 priority.
This means that on the total cart amount, first the rule with priority 1 will be applied, and only after that, an additional 20% off admin carts will be applied.