This pretty planter will be great both for indoors and outdoors. First, tuck the flaps inside the box to make it a little sturdier then lay a few shims along one side of the box to see how long you need them. Mark them with a pencil then trim the thin side of the shim with a pair of kitchen shears. Once you have all of the shims trimmed down to size, add a little E6000 to the backs and stick them on the box, alternating then end to thick end to add some interest. Once that dried for a few minutes flip the box so that you could see the inside and use your stapler to really make the shims stay in place. Keep reading the tutorial in the source.