Non-Inverting Opamp Interactive Simulation
The zener diodes protect the opamp inputs, R1 limits current during high voltage inputs and R1 and C1 form a filter to remove ac components C1 should be a plastic type as ceramic and electrolytic caps are leaky. A large C1 will slow the response time, the sum of Ri + Rf should be greater than 5k so that output is not loaded. also do not connect output to voltages more than vcc/vdd it will blow Opamp.
Vout = Vin * (Rf + Ri) / RiRelated Reading
Noninverting Amplifier - Circuit Design Tutor