What is the function of this circuit? (Included an op-amp, capacitors and resistors)
The large amount of positive feedback gives a strong hint, but if you change the opamp to something slightly more sensible than a 741 and run it through a simulator then you can observe its behavior:







simulate this circuit &ndash; Schematic created using CircuitLab

Its function appears to be to filter and shape a low-ish frequency input signal into an output square wave.
There's some simple low-pass filtering going on with R2, C1, C3 and C2 more-or-less 'shorts' the opamp's inputs at 'high' frequencies.
The feedback resistor R4, along with voltage divider R1 + R3 create a 'Schmitt Trigger' behavior due to R4's positive feedback - ensuring that the output will be driven either 'high' or 'low' with no stable state in between.