You use the liners dark side up!
They are also great if you need to use diaper cream - but be sure to wash off any residue before combining with your main diaper laundry to prevent repelling issues.
They are a beautiful combination of 50% bamboo and 50% polyester that pulls in liquid fast. You'll find the same great material on the top of our boosters, cloth menstrual pads, incontinence pads, and the underside of our small Tank Insert (to help distribute liquid across the large insert).