A very interesting and wide-ranging Mola site on the Web is that of Sherry Thorup , the gallery is lovely and she also has a Bulletin Board for Mola enthusiasts . Rather than putting small pieces of fabric on top of larger pieces and sewing them down as is done in regular applique, reverse applique is done by layer fabrics and cutting through the top layers to expose the underlying fabrics. This image shows 5 layers basted together and the design sketched on the top, red layer. Sherry has an excellent description of Making a Mola at her site which will explain things well. Here is another set of photos showing the making of a mola.
Molas are a fun project for adults and children, alike.
They are popular with teachers, see these examples made by a 5th grade class in Austin, Texas where they made the molas from paper. Bob and Elizabeth Gibson give a list of recommended reading on Molas on their Web site. The Gibson's have very interesting images of their mola collection on their Web site , unfortunately they used GIFs instead of jpg's so the images are very large for downloading, but worth the wait. There are several sites for buying molas on the Web. If you check the Board on Sherry's site I mention above you'll see comments from other vendors of Molas.