if you want to know how an op-amp works in detail, then read this:
READ!!!. if you want a long story short;
most op-amps can handle a dual rail power supply. when the non-inverting (+) input is higher than the inverting (-) input then the output is high. depending on weather the op-amp is on a dual rail power supply or not, 2 different things may happen;
1.)
Dual Rail: if the op-amp is on a dual rail power supply, then when the inverting input is higher than the non-inverting input then the output will read a - voltage in respect to ground (the op-amp is trying to allow current to flow from ground to the - voltage source.
2.)
Single Rail: if the op-amp is on a single rail power supply, then when the inverting input is higher than the non-inverting input, the output will be 0V.
see that 30pF capacitor? that capacitor is in most op-amps, but it's value may vary depending on the op-amp. this capacitor causes what's called a
slew rate in the op-amp. the slew rate is simply referring to the frequency response of the op-amp. as a rule of thumb as the frequency increases, the response of the op-amp decreases. once you pass a certain point then the op-amp stops responding all together. for the 741 operational amplifier, which is the one in both of my images, the drop out frequency is about 1MHz. if you have an op-amp and you want to know what the characteristics of it are; you can look it up on this site:
LOOK IT UP!!!