After you find an image that you like, trace it onto the non-shiny side of the freezer paper. Cut the stencil out using an X-acto knife. I cut carefully, so that I would have one solid camel that I could use for other shirts.
After your stencil is cut out, position it onto a shirt, shiny side down.
With the iron on its hottest dry setting, iron the stencil onto the shirt. Make sure that all edges are securely adhered to the fabric. You can't see it, but I have a piece of freezer paper inside the shirt, kind of making a freezer paper "sandwich", with the camel outline as the "filling". This prevents the fabric from pulling out of shape when you apply the paint, and it keeps any paint from soaking through to the fabric at the back of the shirt.
Once the stencil cools a bit, apply your fabric paint. Be sure to pounce in an up-and-down motion, not in a side-to-side sweeping way. This ensures that you don't accidentally shove any paint under the freezer paper. It's on securely, but I'm sure that if you pushed at an angle, you could get some paint under the stencil. If you noticed, yes, it is a different shirt. I made five of them, so I took the best pictures from each step.
Allow the paint to dry. Depending on the thickness of the paint, this could take several hours.
Once the paint is dry, carefully peel off the freezer paper from the stencil and from the inside of the shirt. If you notice that the paint wants to pull up with the paper, it isn't dry enough. Be patient and wait a little longer. The black fabric paint covered this shirt thoroughly, with no shirt color showing through, so it dried quickly.
Trying to cover a blue shirt with a solid yellow color wasn't as successful. I put on a lot of yellow paint, so it took a lot longer to dry. I had to peel the paper off very slowly on this one, because the paint wanted to stretch and pull off with the paper.
The almost-finished product.
When your stencil is completely dry, it needs to be heat set to help the paint to stay on the shirt after it's washed. You can do this several ways: you can turn the shirt inside out, put a hand towel inside the shirt to protect any bits of ink from transferring onto the back of the shirt, then iron the back side of the image. Or, you can put a handkerchief or napkin over the image and iron it that way. The iron should be on its hottest setting. Iron the image for 3-5 minutes, taking care not to scorch the fabric. I've read that some people heat set their stencils by putting them in the oven at 350 degrees for 15 minutes, or by sticking them in the dryer at the highest setting for an hour. I've only done the ironing method, so I can't say how the other ways would work out.
Here are the stencils I made using the camels I had carefully cut out.
