Before staining, I sanded the shelves to smooth out the edges and corners. After staining the shelf with Minwax Dark Walnut, I then just slid them on to the supports. The fit was perfect and snug! I then realized after putting weight on these, I needed to add more support by adding a 1 1/2" screw into the top of the shelf into the support. I drilled this out first, and then sent the screw through.
I love these shelves because they use all wood unlike some of the other tutorials I saw that use plywood for the underside. Plywood is expensive especially when you won't be using the whole sheet. Making them this way, you just need one 1x6 at 6' to make one shelf. 🙂