The diagram shows a position from the Sicilian Defense. It's called the Scheveningen Variation : 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6. The same position can be reached by switching Black's second and fifth moves : 1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 d6. Chess opening are full of transpositions like this. While the move order is important for steering into openings you like and away from openings you don't like, the position on the board can be evaluated without knowing its history.
Let's count the developing moves. White has moved two Pawns to let the Bishops out and has moved two Knights. That makes four developing moves. We know that White has made five moves. The other move was 4.Nxd4, which was necessary to recapture the Pawn. Some players would say that 4.Nxd4 was also a developing move, because it brought the Knight to the center. We're not going to count that here. We're only interested that the Knight has moved once.
For Black, we count two Pawn moves and one Knight move. Black has played three developing moves out of the first five moves. The two non-developing moves were 1...c5 and 3...cxd4. This doesn't mean they were bad moves. They were among the best moves on the board when they were played. If you're not convinced, just take our word for now. White is ahead in development and has the next move.
[See also Sicilian Defense - 2...d6 Variations.]
