Once you have installed ROS, you're probably be thinking, OK, I have installed it, so now what? In this chapter, you will learn the structure of ROS and the parts it is made up of. Furthermore, you will start to create nodes and packages and use ROS with examples using Turtlesim.

The ROS architecture has been designed and divided into three sections or levels
of concepts:

• The Filesystem level
• The Computation Graph level
• The Community level

The first level is the Filesystem level. In this level, a group of concepts are used to explain how ROS is internally formed, the folder structure, and the minimum number of files that it needs to work.

The second level is the Computation Graph level, where communication between processes and systems happens. In this section, we will see all the concepts and mechanisms that ROS has to set up systems, handle all the processes, and communicate with more than a single computer, and so on.

The third level is the Community level, which comprises a set of tools and concepts to share knowledge, algorithms, and code between developers. This level is of great importance; as with most open source software projects, having a strong community not only improves the ability of newcomers to understand the intricacies of the software, as well as solve the most common issues, it is also the main force driving its growth.