. In front of you should be the large folded rectangle your using for the outside of your bag. Lay it on the table with the folded end towards you. I like to pin this fold down to help hold it steady.
Step 2.1 Fold down the top layer of your rectangle like you see in this picture. The amount of overlap you create will determine the size of the bottom of your bag. For instance, in this picture the overlap is approximately 3", so my bag will have a bottom that is 6" across. Pin down the top of this fold as well. You can see my pin in the picture
Step 3 Sew up the sides (over the folds you made). When you flip your bag out you will have nice boxed out corners like this!
Step 4 Repeat Steps 2 and 3 for your lining. If you would like a pocket inside your tote bag, sew it in first. Making a pocket is simply a matter of sewing two rectangles together (right-sides together). Leave a small gap to turn it inside out from and then top stitch it to the right-side of your lining.
Step 6 Pull your bag through the gap then tuck your lining inside. Your bag should now be right-side out and looking like a tote bag! Top-stitch all the way around the top, closing the gap you left. I pulled my lining fabric down a little so there would be a red border on the top, but you don't have to do that.
Attach your straps. You can use all kinds of things for straps, but to make it super strong, sewing it like you see in this picture works well (sew a box with an X in it). I made my straps and eye-balled how long to make them and where to attach them to my bag. You can insert your straps earlier to have them sewn in between your outside and lining fabrics, but I like to attach them last because I have an easier time lining them up. Here is my tutorial on how to make straps.
If you have any questions about this, feel free to email me, or contact me on Facebook.