Resource management in Fog computing is very complicated as it engages significant number of diverse and resource constraint Fog nodes to meet computational demand of IoT-enabled systems in distributed manner. Its integration with Cloud triggers further difficulties in combined resource management. Different sensing frequency of IoT devices, distributed application structure and their coordination also influence resource management in Fog computing environment. For advancement of Fog and its resource management, the necessity of extensive research in beyond question. To develop and evaluate different ideas and resource management policies, empirical analysis on Fog environment is the key. Since Fog computing environment incorporates IoT devices, Fog nodes and Cloud datacenters along with huge amount of IoT-data and distributed applications, real-world implementation of Fog environment for research will be very costly. Moreover, modification of any entity in real-world Fog environment will be tedious. In this circumstance, simulation of Fog computing environment can be very helpful. Simulation toolkits not only provide frameworks to design customized experiment environment but also assist in repeatable evaluation. In this chapter we focus on delivering a tutorial on iFogSim toolkit for modelling and simulating Fog computing environments. We believe this chapter will offer researchers a simplified way to apply iFogSim in their research works.