It's quite simple to make a g-bag. You need very little sewing experience. Just keep in mind the basic sewing mantra: "Right sides together," and give a moment of thought to the larger picture with each seam, and you won't be forced to use your seam ripper too many times!
Start with four 12" x 12" squares, two each of coordinating fabrics. In addition, cut four 12" strips about 2-3" wide, 2 of each fabric. (Note: each piece of fabric in this photo has a second, identical piece underneath it.)
MAKING THE HANDLES
Make two pairs of coordinating strips, composed of one strip of each fabric. Place right sides together and sew a straight 12" seam along the edge.Then, using your iron, press the straps into their final configuration:
Top stitch along both sides of the straps, using a coordinating thread color if possible.
MAKING THE BAG
Place right sides together of the 12 x 12" squares of the same fabric. Sew along three edges.
Open up the bag and fold one side seam to align with the bottom seam as shown in the photo below. Notice the 45-degree angles. Pin in place. With a ruler, draw a line perpendicular to the seams at the place where the line is 4" wide.
Do this on both sides, and sew a seam along each line. (For a larger bag with heavier fabric, you would clip the "ears", but I don't bother with the g-bag).
Turn one of the bags right-side-out, and put it inside the other bag, right sides together. Align side seams and lay flat. Then, pin one handle at a time to the top piece only, in the space between the two right sides. Only the ends will stick out; the loops will be hidden. Aim for the outside of the handle being 3" from the side seam. When you are done, there should be four pins attaching each end of each handle to the outer bag.
Sew all the way around the bag opening. Leave a 4 to 6" gap between the start and end of the seam. (At this point I evaluate whether I have to adjust a seam to make the bags "fit" each other. If they don't, reduce the size of the larger side by sewing a second side seam just inside the existing one, angling it down to meet the existing seam. This is called "cheating" or "fudging". It is perfectly fine.)
Turn the bag right side out, tucking one bag inside of the other. Stitch a topstitch seam close to the edge around the entire bag.
Tomorrow, I will give you some ideas about where to obtain the fabrics for your g-bag. By the way, feel free to call it an m-bag, b-bag or k-bag, as the case may be. It's all yours!