Freezer paper is wonderful! One side is plain paper. The other side has a waxy finish. I found it in my grocery store next to the aluminum foil. When ironed the waxy finish makes the paper stick, but it is easily removable. Here's how I used it to make this cute shirt for my daughter.
2. Cut out your stencil.
3. Iron it on. I used the cotton setting without any steam. Be creative you can iron it onto a pillowcase, a t-shirt (preshrunk), a book bag, a quilt block, oh the possibilities.....
4. Pick your paint. I used regular acrylic paint mixed with fabric medium or you can use fabric paint. In my picture the fabric medium is white. I choose purple paint and added a little silver paint for sparkle. Mix the fabric medium with the paint as directed on the bottle. Mine said a 1:2 ratio of fabric medium to acrylic paint.
5. Put another piece of freezer paper or a piece of wax paper under the area you will be stenciling to prevent paint from getting on other surfaces like the other side of your shirt. Use a brush of some sort to dab the paint onto your shirt. If you have to use several layers to get adequate coverage be sure to dab and not brush the paint so that it will stay within your stencil. I've only had problems with that on a shirt that needed 6 layers of paint i.e. don't try to paint white on a royal blue shirt.
7. Remove the freezer paper by pulling slowly from one corner.
8. Iron on low for 20 seconds or so to set the paint. Use an ironing cloth to protect your iron. If you start to smell the paint you have definitely ironed it long enough (next time not quite so long).
9. Wash as usual. I try to turn the shirt inside out before washing but that probably isn't absolutely necessary.