In addition to being a type of jewlry necklace chain, box chain is a type of chainmail weave that, rather than creating "cloth", creates a chain. It is also known as idiot stitch because it looks complicated but is in fact rather easy to do. It is kind of like birdcage. Words cannot describe it, you have to see a picture. But I can try and teach you how to knit it.
1. Close an anchor ring.
2. Close two rings onto the anchor.
3. Close two rings onto the previous two.
4. Now, take the rings in step 3, split them apart, and fold them back about 180 degrees so that they flank the rings in step 2. The ends of the step 2 rings will now be exposed; split them apart a little bit to expose the other ends of the step 3 rings below.
5. Through the step 3 rings, on the ends that you just exposed, close two rings. What you have just done is step 2. Repeat, and have fun.