1. To affix something in(to some surface) with a nail or some similar fastener. A noun or pronoun can be used between "nail" and "in." I tried nailing the picture frame in, but it was too heavy for the hollow wall to hold. After you've finished nailing these wooden beams in, you can give the whole thing a fresh coat of paint.

2. To drive a nail or some similar fastener in(to some surface). A noun or pronoun can be used between "nail" and "in." Here, take these and nail them in to hold this piece of wood up. Why on earth would you try to nailing in screws like that? All you'll do is damage both the wood and the screws.