To evaluate the expression \( fg - g \) for \( f = -2 \) and \( g = -1 \), we first need to compute the product \( fg \):
\[ fg = (-2)(-1) = 2 \]
Now, substitute \( fg \) into the expression:
\[ fg - g = 2 - (-1) \]
Subtracting a negative number is the same as adding the positive equivalent:
\[ 2 - (-1) = 2 + 1 = 3 \]
Thus, the value of the expression \( fg - g \) is:
\[ \boxed{3} \]