How does this Op Amp affect voltage?
This diagram explains everything 



At DC the capacitor reactance is very high (open circuit)\$X_C = \infty \$. 

So, op-amp work as a voltage follower (gain one).

As the input signal frequency increases the capacitor reactance decreases. 

And when \$X_C = (R_1 + R_2) \$ at \$F_1 = \frac{1}{2 \pi C_1 (R_1 + R2)}\$ 

The op-amp voltage gain start to increases and will reach \$ \large (1 +\frac{R_2}{R_1})\$ for signal frequency larger than :

\$\large F_2 = \frac{1}{2 \pi C_1 R_1}\$ When \$X_C &lt; R_1\$