I don't get it.....

I recently moved to france and guitar is different here.
I see nothing with Ab C B G, ect...
They teach with Do Ray Mi...
and I don't get it. I try to play with guys here and tell them a Dm and they have no idea what I'm saying.
Does anyone understand this system?

Yes, it's claasiic notation
C = Do
D = Re
E = Mi
F = Fa
G = Sol
A = La
B = Si = H(german)