Hello!
Rutherford's "gold foil experiment" was used to define why electrons revolve around the nucleus. If you remember, he fired alpha particles (which are already positively charged), and when the particles hit the foil, some of them went through the foil. This was determined that there was possibly another positively charged particle inside the foil that repelled the alpha particles. This was his conclusion that atoms contained a positively charged nucleus.
However, Rutherford did not conclude that electrons orbited (revolved) around the nucleus. He did think about it, but it wasn't determined until Niels Bohr came around and determined that electrons revolved around the nucleus.
Based on the "Bohr's model," which depicts a planetary-like movement for the electrons to orbit around the center of the atom, which is the nucleus. He determined this based on the discrete energy levels fixated at each orbit. He found out that at different orbitals (image rings around the solar system where Mercury is first, followed by Venus, Earth, Mars, etc.), each electron had an additional amount of energy.
How could he have measured the energy? Well, when an electron jumps from a higher energy level (farther orbital from the nucleus) to a lower energy level (closer orbital from the nucleus) - like a person moving from Earth to Venus - that energy is released in the form of photons (light particles). Different energy levels produce different amounts of energy, which can be detected by the luminosity of the photons.
