The personal challenge for May makes use of your quilted piece from last month. If you didn't practice your machine quilting, you can still do it and then make the bag.
These are very loose instructions. There are enough bag makers in the group to get help if you need it.
Take your quilted piece and "square it up" -- going for clean lines, not perfection here. If you have a serger or overlock stitch, go around three sides of the panel (sides and bottom). If not, or if you want a cleaner look inside, then you can either make a lining, or do Hong Kong seams (essentially narrow single fold bias enclosing the sides/bottom of the piece) or French seams (but that will be bulky for a later step...may want to reconsider that, but it is doable).
Then fold the piece in half, Right Sides Together, and sew the short side and bottom of the bag with a generous 1/4" to 1/2" seam allowance (or do the French seam if you'd prefer).
Bind the top, same as you would a quilt. Gives a nice finish!
Box the corners -- depth is whatever you'd like. Generally, I go for a visually pleasing proportion, which allows you to play around with the look. That just means that it depends on what purpose the bag has. If I want to carry bulky things, like quilts, etc., I go a little deeper (4" deep or so). If it's for cutting mat/rulers/fabric, then a narrower depth (up to 2").
Attach handles -- length and placement is personal preference. I usually figure out the length I want by trial. These are added last since placement depends on the depth of the bag.