An introduction to the operation of quantum-dot cellular automata is presented here. Quantum-dot cellular automata (QCA) is a transistorless computation paradigm that addresses the issues of device density and interconnection. It is explained here how Quantum-Dots are used as basic building blocks for this new technology. Mapping of the existing technology to this new paradigm necessitates bringing in the QCA structures that can perform all logic operations that are executed in the current technology. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. QCA is exploited here to perform quantum computing and classical computing.