You need old greeting cards or other cardstock or heavy paper and scissors. (That's all, no glue or tape!)
For your first attempt, just use cardstock.
Cut 2 squares. The square for the top should be 1/4" larger than the square for the bottom of the box. (I used a 4 1/4" square and a 4" square.) On the backside of each square, draw diagonal lines from each opposing corner so that you can find the center of the square. Fold each corner in to the center point.
(I drew lines on all of the folds so that you could see them. Don't do this on your box.
Now you are going to make 4 cuts as shown in dark lines below. Be sure to stop exactly where shown.
Now you have 2 sides that are triangles and two that are squares with small triangles on top. Fold the tips of the large triangle sides to the center of the box. Now, on the second folded line, fold up 90 degrees. Fold the flaps in toward the opposite side. As you repeat for both sides, these flaps will overlap.
The next step is hard to explain, so here is a quick video to show how to do it:
You are done! Repeat with the smaller square and now you have a top and bottom. You could make a series of nesting boxes by decreasing the size of the square by 1/4" each time.
Now... to use those cards. Cut a template square for the top. Usually 4 1/4" will work, but you might need to vary it depending on the size of your card. Make all of the folds in your box, but don't make the cuts.
You will see a center box in the template. Carefully cut out that center box. Now you will be able to use this a frame to pick out the prettiest part of the card for your box.
There is really no limit on how big you can make these boxes. You could use poster board and make a giant one! If you do, send us a picture!