There are two different way to make a stencil. One way is to use your Cricut, if you have one. Using your Cricut, you can have your Cricut cut out your design onto the freezer paper, saving you a lot of time.
Another way that you can do this project without a Cricut is to find the picture that you want to paint on the computer. Print the picture out as big as you want it. Then, take a piece of freezer paper (making sure the glossy side is down on the picture), big enough to cover the picture. Using a pen, trace the picture onto the freezer paper. Once you are finished, lay a cutting board under the freezer paper and cut the stencil out using an exacto knife. You will want to make sure that the stencil portion stays in tack as that is what you will be using when you paint.
(Continue here for both ways) When the stencil is completely cut out, place it where you want it. Using a hot iron, iron the freezer paper onto the fabric., glossy side down. You will want to make sure that you iron it on completely and it is sealed all the way around. If the stencil isn't, paint will seep through where you don't want it. Put a magazine between the layers if painting on clothing. Paint using permanent fabric paint, completely covering any white in the stencil. You will most likely need to do more than one coat. To speed the process up, blow dry between coats. After 4-5 hours, remove stencil.
Flower stencil created using my Cricut
Detroit Lion stencil using an exacto knife