user26393: 
Hi I am trying to learn chess, and when I review my moves, I just don't understand how Nd4 is a good move and how nh4 is a blunder.
Thanks.

user924: 14.Nxd4 takes a pawn on d4, and it attacks the bishop on h5. So if black takes back with 14...cxd4, then white has 15.Bxh5, leaving white a pawn up (knights and bishops have roughly the same value). And if black wants to avoid this with 14...Bxe2, white can take back with the knight on d4 (15.Nxe2) so that it is safe too; again, white wins a pawn. And if black retreats the bishop, white retreats the knight, and is again up a pawn.
14.Nh4 does not win a pawn, so that already makes it a bad move when winning a pawn is available. But that is not all: black can first exchange bishops (14...Bxe2, forcing 15.Qxe2) and then fork the bishop on f4 and knight on h4 with 15...g5, winning a piece and opening lines against the white king.
That makes 14...Nh4 a blunder.
More importantly, I am not a chess.com user, but can't you press on those magnifier icons to see the line the engine has in mind after each move?

26393: <p><a href="https://i.stack.imgur.com/jAiun.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/jAiun.jpg" alt="chess blunders" /></a></p>
<p>Hi I am trying to learn chess, and when I review my moves, I just don't understand how Nd4 is a good move and how nh4 is a blunder.</p>
<p>Thanks.</p>
 924: <p>14.Nxd4 takes a pawn on d4, <em>and</em> it attacks the bishop on h5. So if black takes back with 14...cxd4, then white has 15.Bxh5, leaving white a pawn up (knights and bishops have roughly the same value). And if black wants to avoid this with 14...Bxe2, white can take back with the knight on d4 (15.Nxe2) so that it is safe too; again, white wins a pawn. And if black retreats the bishop, white retreats the knight, and is again up a pawn.</p>
<p>14.Nh4 does not win a pawn, so that already makes it a bad move when winning a pawn is available. But that is not all: black can first exchange bishops (14...Bxe2, forcing 15.Qxe2) and then <em>fork</em> the bishop on f4 and knight on h4 with 15...g5, winning a piece and opening lines against the white king.</p>
<p>That makes 14...Nh4 a blunder.</p>
<p>More importantly, I am not a chess.com user, but can't you press on those magnifier icons to see the line the engine has in mind after each move?</p>
