The first thing you want to do is find a decently heavy flat rock.
A log would work as well, however a rock is easier to work with. The weight and size of the rock all depends on what you are trying to catch. For example, if you are trying to catch a mouse, you can use a pretty small light weight rock compared to the size of one used to catch a raccoon. My personal animal of choice, is the squirrel; they are so cute and tasty.
The second thing is to find two sticks, one longer and slimmer than the other.
The long slim stick will end up being pinned up against the rock (he rock being lifted up at about a 30 degree angle) by the smaller beefier one. The end of the slimmer stick, is where the bait will be.
You can get creative with the bait, using whatever you think may attract the critter you seek. For squirrels I usually use some kind of nut. To get the bait to stay on the end of the stick, I usually make a split down the middle of the end of the stick, and then wedge the bait in between. This way the wood will clamp down on the bait, making it hard to pull out.
Once these steps are complete, it is time to put it all together. For the best results, you must know the animal you wish to catch. Know where he spends his time. It is recommended that you build the trap in the area where the creature hangs out, because it will be more likely to find the trap. Once you have found this place, begin to set up the trap. Lift up one end of the rock (lifting it to the desired height) then with your other hand, place the two sticks underneath it so that they are then supporting the rock. BE CAREFULL WHEN LIFTING THE ROCK!!!!! It is easy to drop the lifted end of the rock on your fingers. Make sure that the surface you build on is solid. If you build it on soft ground, the animal may not die right away when caught and will then be suffering for however long. That wouldn't be respectful to the animal. I like to set up my deadfall traps on fallen trees or hard ground to ensure that the animal dies right away and is not in long agony. Check the trap ever hour or so. You don't want to go too long without checking the trap, because the animal might have been caught for a long time and its body might be really stiff and icky.
This trap is super effective and really easy to make. Enjoy the trapping!!!