It uses an Op-amp to realize an active filter.
The cutoff frequency (in hertz) is defined as:
$ f_c = \frac{1}{2\pi R_2 C}$
The gain in the passband is −R2/R1, and the stopband drops off at −6 dB per octave (that is −20 dB per decade) as it is a first-order filter.
