If your refrigerator smells bad, first make sure it's not coming from anything inside the refrigerator. Sometimes spoiled food can make your refrigerator smell bad; and if you're not an expert, the smell can seem similar to that of leaking gas, which is what freon smells like. Clean out your refrigerator and get rid of anything that's moldy or has been around for too long. If the smell persists and doesn't seem to be coming from inside the refrigerator, it probably is a freon leak.
Freon gas can be hazardous to your skin and your eyes. Thus, before beginning to search for and fix a freon leak, you should put on goggles and rubber gloves. You will definitely need to unplug your refrigerator, before you do any work on it, to reduce the risk of injury or death by electrical shock.
Most freon leaks are in the rubber hoses underneath the refrigerator. Once you have your safety gear on and the refrigerator is empty, have an assistant tilt it forward so you can inspect the hoses with a flashlight. Look for any nicks, cracks or tears in the hoses and notice where the smell is strongest. You can patch the hoses with a rubber patch kit, available in most home improvement stores.
Rubber patch kits are meant to be temporary solutions -- they won't fix the problem permanently. Since freon is toxic, you don't want a leak getting into the air around you or into the food in your refrigerator. Thus, once you've found the leak and patched it, you should contact a repair technician to service your refrigerator and find a more permanent solution to the freon leak.