Device-to-device communications underlaying LTE-Advanced wireless networks reuse cellular spectrum to establish direct links between users without traversing the base stations or the cellular network. In this paradigm, there is a need to allocate the resources with a view to maximizing the utility (e.g., the total throughput) and mitigating the interference caused by sharing the same spectrum between cellular users and D2D pairs. This article, which is tutorial in nature, proposes a scheme for maximizing the total number of active D2D pairs and reused channels while minimizing the aggregate transmit power of cellular users and D2D pairs and maintaining their required QoS to the extent possible. This reduces the load on base stations, lessens power consumption, and improves spectrum efficiency beyond the conventional cellular frequency reuse schemes. Unlike many existing works that assume a single cell, we consider a multi-cell scenario in which the transmitter and the receiver of each D2D pair can be in the same cell or in different cells, and each user can simultaneously transmit over multiple reused channels. The allocation is done via a centralized baseband processing in the cloud radio access network architecture. Simulations show that via our proposed scheme, more users (both cellular users and D2D pairs) can simultaneously communicate, and the total system throughput is also significantly increased.