Interpreting "missed win"

Hello everyone.  I'm a beginner learning how to play chess and I found this website's analysis to be a great tool to improve my play.  However, some analysis confuses me.  This move, for example, was registered by the chess computer as a "missed win".  

The last move played was cxd4.  a black pawn was on the d4 square.  the computer, in all of its great wisdom, has registered this as a "missed win", instead suggesting Nxd4.  This gives me slightly more control over the center, but it does not win any material, as the opposing Queen has many safe spaces to return to, and all the pawns that the knight threatens on d4 are well protected.  The knight is also hanging on that square because no pieces are protecting it.  Can anyone tell me if I'm interpreting this correctly?

Thanks!

A 'missed win' is a move which leads to checkmate or a sizeable advantage, either materially or positionally. Without analysing in great detail this position Nxd4 forces the queen to move away obviously as you say. I think the point is that white wants Ne4, threatening Nf6+ or Nd6+ and other nasty threats against the black king, which is still stuck in the centre, plus black has hardly developed. There could even be Rhe1 with some sac on e6. Anyway, the specific analysis is of course important if you can see it, but the choice between cxd4 and Nxd4 is quite clear even if you can't see a winning/advantageous line. Whites pieces are beautiful compared to blacks, you increase this advantage by going Nxd4 forcing a queen move which doesn't help black develop. Then after seeing where black puts the queen you can think again. cxd4 by contrast allows black a 'free' move to do something, gives white an isolated pawn on d4 (potential weakness), exposes the white king slightly on the c file. It's not a disaster as blacks position is still unpleasant but Nxd4 is clearly much better, even if the 'win' is beyond your vision. Hit the queen, see what happens, look for the next move that looks strong.