Start with a prepped t-shirt that is ready to be turned into a bag (https://sites.google.com/view/howtoprepat-shirttoturnintoa/home ). It should look something like this....
the first step now is to turn the shirt inside out and line up the edges on the bottom. this is going to be how we start the sewing process, by sewing the bottom it will make it be able to hold things. TIP: hold the shirt by the shoulders and shake it out to line everything up.
Now set up your sewing machine! I typically sew there bags with either white or black thread but use whatever color you would like. Make sure your machine is threaded and then turn the stitch to a zig zag stitch. On my machine it is stitch number 3. WHY: the use of a zig zag stitch gives more strength to the seam allowing the finished bag to hold more and be more durable.
Lets start sewing!! With the bottom edges lined up sew a line across the bottom fully making sure to back stitch at the start and at the end. I personally like sewing over the preexisting seam line because it is a straight line to follow.
Once the bottom has fully been sewn you can turn the bag back to the right side out.
For the next steps we are going to be sewing around the arms and neckline due to all the turns I recommend taking your time and going slow. You may have to pivot a couple of times to get around it fully. I typically start with the right outside arm and go around it first. I start a little bit before the arm seams and fold the cut edge in about an inch to make a clean edge. Still with the zig zag stitch you are going to sew fully around the hole and back stitch at the start and end. Your stitch should start and end at the same spot.
I next move to the neckline to do the same thing. Still with the zig zag stitch you are going to sew fully around the neckline and back stitch starting and ending in the same spot. TIP: I have found it is easier to sew to the back to starting on the back side doing it before going around to the front.
You are going to repeat the arm steps on the other arm now. TIP: I have also found that is is easier to do this like the neckline starting with the back and moving to the front after.
Now you should have a completed bag!! Enjoy!