(There is a really good one here.)
The basics are, you find an image and trace it onto freezer paper (which you can buy at the grocery store). Cut the image out of the freezer paper to turn it into a stencil. Iron the freezer paper to a garment and it sticks with a great seal. Paint or blot the stencil with fabric paint (I bought some at Michaels and Walmart). Then peel off the freezer paper and TADAH!
Here is a shirt we made Delilah using freezer paper as a stencil. Daddy picked the design of course.
So Delilah has a collection of stencilled band Tshirts including Kiss, NIN, and Run DMC. Think her Father's taste in music will rub off? Hmmmm....I may have to put some thought into this and make some shirts with The Beatles stuff on them!