This DIY reusable grocery bag fromDaisy Love Country lifeon Youtube will surely help you a lot.
Watch the video tutorial below to learn.
Spread it with the wrong side facing the top.

Image credits: Daisy Love Country life via Youtube
Fold it horizontally in 9 cm width.
Do this on the other side as well.
Sew both folded sides in the middle, with a 1 cm lock stitch.

After this, flip the bag inside out.
Get a template with 16 cm x 14 cm measurements.
Place this on the top part of the bag, then trace it out.

Cut the lines using scissors.
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Step 2
Get another fabric with plain color at 3.5 cm in width.
Fold this fabric and attach it to the edges of the handle by sewing it.
Next, sew both the top of the bag handle.
After this, fold both the handle inwards, then sew to attach both sides.
Your bag is now finished.