Learn by experimenting with an op amp on this virtual electronics bench. You have a function generator, op amp modeler, and an oscilloscope. The function generator's output goes to the op amp model's input and to o-scope Channel 1. The op amp model's output goes to o-scope Channel 2. Rate increases or decreases the cycle rate. Experiment, learn, have fun. Click any resistor to change it's value.
This is a very idealized model and you will definitely see variations on the bench. Here are some examples: The op amp's positive and negative saturation output voltages are assumed to be of the same magnitude. The resistors are exact values without tolerance variations. The op amp has the qualities of the perfect op amp: infinite input impedance, zero output impedance, perfect linearity and perfect DC offset and gain and no leakages or offsets. But for quickly coming up with offsets and gains this is a cool little tool. I may add some enhancements to make it more useful.