Energy is defined as work, and electric potential energy (U) is expressed as U = Vq, where V is electric potential and q is charge. The relationship between work (W = Fd) and electric potential energy can be understood through their common unit, Joules, which equals Newton-meters. This connection is reinforced by recognizing that volts can be expressed as Joules per Coulomb, allowing for the cancellation of units to show that electric potential energy also results in Joules. The discussion emphasizes the similarity between gravitational potential energy and electrostatic potential energy, with mass being replaced by charge. Overall, the conversation highlights the importance of building on existing knowledge to understand complex concepts in physics.