I grew up summering on an island off the coast of Maine, and we liked to harvest our own seafood. Now, we weren't allowed to take lobsters--you need a license for that and it takes five years of permanent residency--but you could take clams and mussels (though today you're supposed to have a clamming license but no one can see what we're doing and only take as much as we need).
Finding a Clam
You're looking for an oval hole under a rock or in the mud. A square one is not what you want. Take your clam rake and dig like hell. The clams will race you; they are faster than you think.
When you get them, put them in your clam hod. That's usually a wooden rectangular basket that will hold about half a bushel. Wash them out in the ocean before you...
Preparing Clams For Steaming or Frying
Put them in a bucket of fresh water, to which about a cup or two of cornmeal has been added. This will make the clams purge and they will eat the cornmeal. You may scrub them afterwards.
Now you have a decision to make. Do you want to steam them or fry them? If you want to steam them, the simplest way is to cover them in seawater in a shallow frying pan and cook them until they open, and then serve them with drawn butter and the juice from the pan.
Alternately, you could take them out of the shell, dredge them in flour and corn meal and fry them in lard, serving them in a roll or with tartar sauce.
And that is what you do with a clam.