The functionality requires the Volume Discounts add-on to be installed and enabled.
A store admin can set up membership-specific discounts in the section Discounts -> Volume Discounts of your store Admin area.
The process of setting up a membership-specific volume discount is relatively straightforward:
In the Volume Discounts section of your store's Admin area (Discounts > Volume discounts), add a new discount, as described here.
Specify the subtotal amount starting from which the discount will be available. Set the discount amount (select an absolute value or a percentage) and select the membership level that a customer must have to use the discount.
Save your changes.
More info on volume discounts you can find here.