I could not live without my light box after the wonders that it did for me in Hong Kong, so the first thing I did when I got to Vancouver was to make one for my home there. This time I took step by steps, I hope this helps.
Find a decent sized paper box that you no longer need.
Make borders around 3 sides of the box (I just used the thickness of my ruler since that make it easier for me)
Use a knife and cut around the border like the picture above.
Tape tissue paper down to cover the openings
A few pictures just to show that you don't need to do a great job a taping to get a good lightbox
Should look something like this in the end, now you just have to pick a background that you like, but you all know what mine looks like :)
Enjoy your finished product (I know I need to use a better light, but still a fairly good pic I think)