Here you can see a classic potential divider circuit configuration, where 10V is split into two 5V outputs.
However when you try to draw more and more current off from one of the divider resistors, the voltage balance will be upset the load will get less than 5V.
We can introduce an opamp, where the 5V output is connected to the non-inverting input, and we short the output to the inverting input as feedback. We now create a opamp buffer or voltage follower where the input has very high impedance (think of it as resistance), this barely upset the voltage dividing balance and the opamp can supply the require current to the load independently.
