At first, I tried making it with an old dress, but that attempt didn't work out (I was sewing sort of crookedly), so I moved on to the shirt which ended up working much better because it was stretchy.
There's my sewing machine!
It was a bit tough sewing up the stretchy fabric, but the handy guide that came with the sewing machine helped me with the right settings.
Sewing a non stretchy strap to the stretchy material was kind of difficult. Mr. A suggested we pin the straps all over so that I could sew it on properly. It really helped.
Here's the bag all finished!