I helped my sister make some shirts for her and her friend.
Step 1: Supplies
All you will really need for this project is some cheap white tee shirts (we went to Walgreens), some cardboard,an old knife, some thumb tacks, a sharpie, and a few cans of spray paint.
Step 2: Set up
First cut out a piece of cardboard that is a little smaller than the shirt. Stick the cardboard inside the shirt and use the tacks to smooth out the front. Then cut out a shape of something (like a heart!) and tack it onto the outside of the shirt.
Step 3: Painting
Now you just lightly and evenly mist the front (or back) of the shirt with whatever paint you have. Let it dry for an hour or so then take off the shape. I also sprayed it with some silicon water proofing spray but I don't think it really help. You can try any shapes you want. This shouldn't be too hard cause my sister was able to do it!