Nxd5 means you just traded your bishop for a pawn. That's not usually a good trade.
e6 gains tempo and allows you to remove your bishop from danger with Bc3.
The computer says trading your bishop for the pawn is poor choice.
This is complex and above your rating, but the basic idea is this: black has two pieces attacked. If black saves one, material is close to equal, but the position is crappy. Don't worry about why, thats not the key thing to absorb here. The computer move, by contrast, attacking the white knight threatens to take a white piece **while also protecting the black knight** because if the pawn captures, suddenly his knight is protected! For example, if white plays rxb, black takes the knight, while protecting his knight, and now black is up material. White taking the knight doesn't work either, as after qxn, pxn attacks the white queen, giving black a chance to save the bishop -- again black has both saved a piece, and taken a piece! So white must look at knight moves -- I won't analyze why those aren't good enough for advantage either. At your rating level, I think its sufficient to get the initial concept -- ie that the pawn move threatens to take a white piece, while simultaneously protecting one of blacks's two hanging pieces or gaining an extra turn to save the bishop by taking a piece and thereby also attacking the queen.
Does that make sense? Even the basic concept is a bit advanced for your rating level, but you should be able to understand it if you work through what I'm saying.
@ArtNJ thanks that helped! I was actually looking et e6 in the game but i just thought, I had two hanging pieces, and if I take the pawn he takes my bishop und if I play e6 threaten to take the Knight we'd end up in the same spot, I guess I didnt see that after capturing I would be protecting the knight.
The response by #3 does not completely convince me.
Let's begin with the basics and that's counting your material. After the move 14. bxc5 you are up an exchange and a pawn. To be even more exact, you have a rook and a pawn and they have an extra lightsquared bishop. When you take the pawn, and they take your bishop, you end up with 2 extra pawns and an extra rook, but they have 2 extra bishops. What you need to realize is that 2 pieces for a rook and a pawn sounds like an even trade, but in the middlegame the 2 pieces are often stronger. Bishops are stronger than a knight too. So the position is definitely in your favour, but it's tricky, as the 2 pieces are usually stronger than a rook.
It is only natural though that you try and save your pieces. If you could save both of your pieces, you'd be up an exchange and a pawn after all. 14. ... e6 is a way to do that. If white takes your bishop, you take their knight (even trade) while guarding Ne4. That way you're up the exchange and a pawn. If they move 15. Nb4, you can attack the knight with 15. ... Bc3 which also gets one of your pieces out of jeopardy. If they play 16. Qxe4, which appears to win back the piece AND defend the knight on b4, you can play 16. ... d5! And now suddenly the white queen has no squares to go to that also still protect Nb4, so you will back the piece anyway. This tactic is hard to spot.
My big question about the computer line would actually be why after 14. ... e6, 15. Nb4, Bc3; 16. c6 we're not just taking 16. ... Bxb4. Because if you count, you will see that you're up a full rook by this point and a pawn. We've saved our pieces at this point. So after 16. ... Bxb4, it can continue 17. cxb7, Rb8 18. Qxe4 and now we just move 18. ... Bc5 and we seem to be having an extra exchange. Now, the computer might not like this position, as that far advanced passed pawn on b7, that can't really be attacked and can be defended by white's lightsquared bishop, could be more than enough to compensate for the deficit in material. I would agree with this. It's hard to deal with this pawn.
Instead of letting white have a position with a far advanced passed pawn for just an exchange, the computer prefers to give back the exchange. In the resulting position that the computer gives, you can see that black ends up with an extra pawn and the rest is equal. White doesn't get the advantage of the two pieces for the rook play. That's a clean advantage, much cleaner than your advantage after Nxc5.
So, what should you be able to see of all of this? Well, if two pieces are attacked simultaneously, you should look to see if you can find a way to get both of them into safety. You need to look at forcing moves. So, the idea with e6 is something you should be looking for. It's something that you can miss though. Especially the line 14. ... e6; 15. Nb4, Bc3; 16. Qxe4 and then seeing you can play 16. ...d5 to win back the piece is something you should not be ashamed of missing at your level at all. So, Nxc5 becomes the preferred choice. It doesn't matter that there is a deep tactic in the position that is even better and that the computer spots. That's for when you're stronger.
Now let's ramp up the difficulty and return to your question about evaluating both positions. In the position after 14. ... Nxc5, 15. Rxa1 you can see that white is much more active. So not only does white have the compensation of the 2 pieces for the rook that for the time being should be good for the 2 pieces, but white also has much more active pieces. Your rooks and your queen are doing nothing at all. White has all developed pieces. Now compare this to the position of the computer line with 14. ... e6. after Qxa8. That feels like a good final position for the line. You can see black is only a pawn up and the rest is equal. So no imbalance of the 2 pieces for the rook. Also, in that position, black has the active pieces. So basically in the final position of that line, white has nothing. The difference in activity is visible to everyone. It's hard to evaluate how important activity is. Dynamic advantages are not so easy to play with. That's why it shouldn't have to factor greatly in your own evaluations of the positions just yet. But in the hypothetical situation where you would have seen both lines, going for the computer line looks to be much better, because you have a material advantage AND the dynamic advantage.
Well thank you so much for taking the time @RAU4ever
what's your problem?
As a 700 elo player, I personally want to know about dxc5. e6 makes sense to kick out the knight, but doesn't dxc5 win the pawn? if they chose to retreat the knight, you get the bishop to safety. If they choose to take the bishop, not only do they spend a move moving a rook onto an open file, your queen is much more active after taking the knight.
@Irongine - It is black's turn, but white is attacking two pieces: wRf1--bBa1 and wQe4--bNe4. Black needs to figure out a way to save both pieces. Easy for an engine, not so easy for a human. Your move, 14...dxc5, opens an attack bQd8--wNd5, but it still leaves white free to make both captures, so you need to consider both. Instead of retreating the knight, white can play 15.Qxe4, taking a piece AND guarding the wNd5.
Because winning positions do not always depend on the amount of material. It varies by the positioning, the forced moves (from king checks), checkmate positions, and even the pieces you have traded in (example it's better to have a bishop and a knight rather than a rook and a pawn, even though they are considered to have the same amount of material)
