Knight placement in French Defence

After 1.e4 e6 2. d4 d5

Stockfish says Nd2 is the best move. I just don't understand the significgance between Nc3 and Nd2

Nd2 doesn't interfere with the c-pawn (and basically discourages Bb4), but it interferes with the development of the bishop on c1.  Nd2 is the move that more top-level players are interested in right now.

Using engines on move 3 is a horrible idea anyway, too many ideas for a position so early in the game means that it can't really go with an accurate reading, so practice and modern theory is best.  Besides, the French is one opening that engines do the worst with, so go and look online if you want to understand the opening instead of just reading what a computer spits out at you.  There's also a wonderful thing called Google which takes less time to use (and with better results) than to use an engine and then create this thread, and the Wikipedia article on it also describes the differences between Nd2 and Nc3.

im new to all this, but nd2 is a way to avoid the winawer with 3...bb4. at a lower level many players fear the winawer. arguably 3nc3 is the best move and lets face it, winawer with 7 qg4 is a right laught, long live the poisoned pawn.

ok, my understanding(very limited) is that there are 3 main choices, 3e5, 3nd2 and 3nc3, all of which are supposed to be strong. some of the great players of all time have played nd2 and e5, so fair play to them. I think 3nc3 bb4 is a lot of fun thats all.

Using software on move three isn't a good idea. It's better for use 15th plus moves in game to verify if an idea is tactically sound and not for planning.