In the era of big data, networks are often from multiple sources such as the social networks of diverse platforms (e.g., Facebook, Twitter), protein-protein interaction (PPI) networks of different tissues, transaction networks at multiple financial institutes and knowledge graphs derived from a variety of knowledge bases (e.g., DBpedia, Freebase, etc.). The very first step before exploring insights from these multi-sourced networks is to integrate and unify different networks. In general, network alignment is such a task that aims to uncover the correspondences among nodes across different graphs. The challenges of network alignment include: (1) the heterogeneity of the multi-sourced networks, e.g., different structural patterns, (2) the variety of the real-world networks, e.g., how to leverage the rich contextual information, and (3) the computational complexity. The goal of this tutorial is to (1) provide a comprehensive overview of the recent advances in network alignment, and (2) identify the open challenges and future trends. We believe this can be beneficial to numerous application problems, and attract both researchers and practitioners from both data mining area and other interdisciplinary areas. In particular, we start with introducing the backgrounds, problem definition and key challenges of network alignment. Next, our emphases will be on (1) the recent techniques on addressing network alignment problem and other related problems with a careful balance between the algorithms and applications, and (2) the open challenges and future trends.