Here are the basic instructions for an explosion box.
Using a 12 x 12 cardstock, score in from each side 4 inches and score each corner section as shown.
Fold to create the box.
The lid is made in the same manner but the lid base would need to be 2 mms bigger (this is to allow for the lid to fit with a little wiggle room rather than snug) and the sides are reduced by half or less if desired.
So cut a 8.2 Inch square. e.g. 2 inch side + 4.2 inch base + 2 inch side.
Score from each side 2 inches. Cut out the corners leaving tabs to secure.
The gift box below is made using this base instruction but the corner sections have been completely removed. I hope this is easy to follow. Good luck.