To open the box you pull out on the mantel and the first two courses of bricks above it slide down to allow the top to slide off. The entire box is assembled with just glue. To assemble, start by putting the locking bar in through the top of the lower chimney piece, with the cutout facing towards the center of the box. Glue a dovetail pin into both dovetails and glue the third pin into the locking bar already in the chimney, place the dovetails into the vertical slots inside the lower chimney. With both dovetails in the bottom of the tracks slide the locking bar up a little bit and apply glue to all the pins and the holes in the chimney slider, then press the chimney slider onto the dovetails and the locking bar pins. Make sure it all slides freely. Next, glue the two mantel pins into the mantel keepers and slide the mantel into the box below the mantel slider. Glue the mantel retainers in through the holes inside the lower chimney and make sure everything slides appropriately. The liners should be a friction fit but a little glue will keep them from moving about. The liner is largely there to provide a more finished appearance and also keeps the contents from fouling up the moving bits.