The op-amp is basically a very high gain dc amplifier having a large voltage gain, very high input impedance and low output impedance. The op-amp has a "inverting" or (-) input and "non-inverting" or (+) input and a single output. The op-amp is uses dual power supply in the range of +/- 5 volts to +/- 15 volts. A simple dual polarity power supply is shown in the figure below

In case of opamp, all measurement is carried out with respect to ground and hence ground line is not shown

When signal is applied to non-inverting terminal (+), we get the output of the same polarity as that of the input.

When signal is applied to inverting terminal, we get output with opposite polarity.