compare the practical value of voltages and currents obtained in thevenin equivalent circuit to those measured in the actual circuit

Imagine your circuit sitting inside of a black box. You cannot see inside of the box, all you can do is control what goes in, and measure what comes out. This is the same idea that Thevenin wanted to imply. We can measure each individual component in the circuit, but once they are all combined what will we see? The voltages and currents obtained using a Thevenin equivalent circuit represent the Ohm's law results using equivalent voltages and resistances, instead of individual components.