Birch bark is extremely versatile and resilient. Consequently it can be used for making a lot of different things. You need bark of a certain quality to make this type of box.
Take a long piece of bark and roll it up double. Sew it up with some type of cordage. For such high strain, static applications, split spruce root is ideal.
I had limited amounts of spruce root available this time, so for the rest I used strips of willow bark. The bottom of the box and the top of the lid is doubled with bark in two different directions for added strenght. Stitching across the grain is always important to do when using birch bark. Otherwise the bark will most likely split.
That's the basics of it all, an excellent box for storing all sorts of small items. There are many tips and tricks regarding fitting and similar that doesn't fit in here. A more in depth tutorial will be in the upcoming book(s).