Let us suppose I am a chess beginner. I often lose my games. Well, it depends on the opponent but generally I can hardly win. My problem is I do not know what I should do with my knights.
Usually chess textbooks or people whom I asked for advice tell me, "You must develop your knights very early in the game; it's necessary for castling." After that, they don't give any more useful information.
I simply do not know what to do after I castled... For example, I've played 1. e4 2. Nf3 3. Bc4 4. 0-0. After that, I am stuck. A few times, I tried to be brave and to advance my knight forward in hope of giving a smothered checkmate, but I always had to encounter the opponent's queen, which is extremely powerful. Returning my knight to initial square doesn't make any sense for me. And not making any further moves with my knight seems to be pretty stupid as well.