Have you ever wondered about how those data scientists at Facebook and LinkedIn make friend recommendations? Or how epidemiologists track down patient zero in an outbreak? If so, then this tutorial is for you. In this tutorial, which is Part I of a two-part series, we will use a variety of datasets to help you understand the fundamentals of network thinking, with a particular focus on constructing, summarizing, and visualizing complex networks. With this tutorial, you will be well equipped to explore advanced topics (dynamics on graphs, evolving graphs, and network propagation methods) in Part II.