The Voltage follower uses the output voltage (Vo) as a feedback voltage and its created by shunting the output to the negative inverting terminal (V-), this is going to make that the output is going to the same voltage as the input (V-) terminal and the difference between the voltage at the input of the opamp is going to be 0V which lead that the opamp is going to be at equilibrium having the same voltage as the input.
The Opamp is looking always for the voltage between the two terminals (Vi- and Vi+) and is going to adjust the output with what it sees in those terminals.
This way the gain of the opamp is about 1 as can be seen the two waves together (Blue and Green), never more than 5V the positive rail and 0V negative rail but if the input is more than the rail voltage the opamp is going to cut above that value
The impedance of the opamp at the input is the opposite of the output, which means that at the input, there is a high impedance and in the output a low impedance, this circuit allows to create of a voltage buffer and can be used to isolate circuits.
