The code for this section is located in navigation_bot_10 part of an archive. Note that archive includes some additional folders, like maps and worlds, that are used by all projects and therefore are located outside of them. Note also that we use ROS2 Galactic now.
Also note, that the code in this section is suboptimal: we are going to improve it in the next section. However, it is easier to both implement and understand. The next section is built on this basis.