The Tarrasch should be a popular one, the point is kind of to play c4 I think. Here's a website that may help ya.
How do you play with the black pieces in French Defense, Tarrasch Variation?

The idea for Black in the Tarrasch is simple.
1 e4 e6 2.d4 d5 3.Nd2 c5!
Black plays c5 before White commits to e5, which allows White tetrahedron instead of advance, leading to an IQP position,but in return, White's Knight impedes the Bishop which impedes the Rook, so White's play is slow and Black gets good piece activity.
A line I recommend is 4.exd5 exd5 5.Ngf3 Nc6 6.Bb5 Qe7+ 7.Be2 (7.Qe2 is already equal for Black) 7...Qc7 8.O-O Nf6 9.Re1 cxd4 10.Nb3 (10.Bd3+ Be6 is fine for Black) 10...Bb4 11.Bd2 Bxd2 12.Qxd2 O-O and White has at most a teeny tiny advantage. Black should have no problems equalizing.

The idea for Black in the Tarrasch is simple.
1 e4 e6 2.d4 d5 3.Nd2 c5!
Black plays c5 before White commits to e5, which allows White tetrahedron instead of advance, leading to an IQP position,but in return, White's Knight impedes the Bishop which impedes the Rook, so White's play is slow and Black gets good piece activity.
A line I recommend is 4.exd5 exd5 5.Ngf3 Nc6 6.Bb5 Qe7+ 7.Be2 (7.Qe2 is already equal for Black) 7...Qc7 8.O-O Nf6 9.Re1 cxd4 10.Nb3 (10.Bd3+ Be6 is fine for Black) 10...Bb4 11.Bd2 Bxd2 12.Qxd2 O-O and White has at most a teeny tiny advantage. Black should have no problems equalizing.
Thank you very much!

Another good line for black is to take with the Queen on d5 after exd5 . This is recommended by Anish Giri in the Chessable course .

The idea for Black in the Tarrasch is simple.
1 e4 e6 2.d4 d5 3.Nd2 c5!
Black plays c5 before White commits to e5, which allows White tetrahedron instead of advance, leading to an IQP position,but in return, White's Knight impedes the Bishop which impedes the Rook, so White's play is slow and Black gets good piece activity.
A line I recommend is 4.exd5 exd5 5.Ngf3 Nc6 6.Bb5 Qe7+ 7.Be2 (7.Qe2 is already equal for Black) 7...Qc7 8.O-O Nf6 9.Re1 cxd4 10.Nb3 (10.Bd3+ Be6 is fine for Black) 10...Bb4 11.Bd2 Bxd2 12.Qxd2 O-O and White has at most a teeny tiny advantage. Black should have no problems equalizing.
And about The main line Qxd5, what do you think about It?

I recommend the Rubenstein against both Nc3 and Nd2. You very quickly accumulate a big advantage in experience in these positions, because you'll be seeing it way more than your opponents and it's not something that they could overcome by memorizing theory since the game is very positional in nature.
I play the french defence but i don't know the tarrasch variation(1.e4 e6 2.d4 d5 3. Nd2) a lot and i always lose game because of this. It is not a popular openings and when i search online i never get the answer, Please tell me in the comments or give me a link to a website that may help me, Thanks!