Upon successful installation, you will find a new Discount requirement type under Admin Area > Promotions > Discounts, named as Minimum cart subtotal should be x.xx amount.

This discount requirement can be only used with a discount where the Discount type is set to Assigned to order subtotal as displayed in the image.

discount cart subtotal configure

 

As you can see in the below picture, this discount requirement needs you to set a Required cart subtotal amount which will be used to validate this discount against customers cart subtotal amount.

discount cart subtotal requirement

Once saved, the discount requirement will be added to the discount.

discount cart subtotal requirement group

That's all you need to do in order to use this discount requirement in your nopCommerce store.