I have some confusion on this notation
It is written that
An $R -$module $N$ is flat if tensoring with $N$ over $R$ as a functor from $R $ Mod to itself $(-)\otimes_R N: R Mod \to RMod$ is an exact functor ( sends short exact sequences to short exact sequences )
My confusion : Im not getting the meaning of $(-)\otimes_R N?$
My attempt : I was reading Atiyah book .In Atiyah book it is written that
$N$ is flat if $N \to M' \to M'' \to 0$ is any any exact seqence of $A$ modules , then tensored sequence $ 0 \to M' \otimes N \to M \otimes N \to M'' \otimes N \to 0$ is exact.