find and old t-shirt you no longer wear, make sure it is clean and dry.
turn shirt wrong side out, the sleeves need to be cut off then sewn closed also sew the neck opening closed.
then turn the shirt back the other way. the bottom of the shirt should be open.
now stuff the shirt with stuffing from a hobby store or other place that sales sewing or crafting material.
last tuck the tail of the shirt in so it looks like a hem, and sew it closed.