For people learning robotics, the ability to have access to real robots is fun and useful, but not everyone has access to a real robot. This is why simulators exist.
In this chapter you have learned how to create a 3D model of your own robot. This includes a detailed explanation that guides you in the tasks of adding textures and creating joints, and also describes how to move the robot with a node.
Then we have introduced Gazebo, a simulator where you can load the 3D model of your robot and simulate it moving and sensing a virtual world. This simulator is widely used by the ROS community and it already supports many real robots in simulation.
Indeed, we have seen how to re-use parts of other robots to design ours in a nutshell. In particular, ...