So input $= R(s)$ and output $= C(s)$ and forward transfer $= G(s)$ and feedback transfer $= G_2(s)$
deriving feedback now $= G_2(s)C(s)$ forward signal $= R(s) - \text{feedback}$$ =R(s) - G_2(s)C(s)$ output $C(s) = G(s)(R(s) - G_2(s)C(s))$
Now I don't understand this step The text says next is $C(s) = \frac{G(s)}{1 + G_2(s)G(s)}R(s)$