French Defence: Tarrasch Variation / 3....Nf6
This position has some similarities to the Steinitz Variation of the Classical French, however, with their Queen Knight on d2 (instead of c3) White will find it easier to defend their center pawns.
Having the option of supporting their d4-Pawn by playing c3 certainly is a good thing to have, and if things get worse, White can also use both knights to defend d4.
In this variation Black will find it difficult to undermine White's pawn center successfully, at least if they try doing so in a classical / stereotypical way.
After Black's 4. ... Nfd7 White has several ways to play, with 5.Bd3 being the most common choice:
White wants to develop this bishop to a very good diagonal - before they must play Ne2 (in response to Black's upcoming pressure on d4.) 5.f4 is a good alternative for White, which overprotects the e5-Pawn and makes it more difficult for Black to create pressure against e5 (e.g. by playing ...f6).
Moves like 5.c3, 5.Ne2, 5.Ndf3 or 5.Ngf3 are played less often, but aren't bad either.