Tube binding is when you take a square of fabric, cut it on the diagonal, then sew the top & bottom together, roll up and offset the edges and sew a tube. Then, you cut the width of your binding around and off the outside edge of the tube until the fabric is all used up. Kind of hard to describe, but here's a link to instructions.
http://quilting.about.com/od/binding...g_strips_4.htm
I have a card that shows the steps a little more clearly because you mark direction arrows and edge markers before cutting to make sure everything goes back together correctly. That's when I've made mistakes - sewing the triangles together in the wrong way.
The instructions say to mark and cut with scissors, but I've learned to use my rotary cutter and do a little at a time to cut my binding. This is the only way I've ever made binding!
The card also has a whole bunch of squares already figured out for me and saves math. :)