In our created workspace, chapter_4_ws/src, create a package called battery_simulator using the following command:

$ cd ~/chapter_4_ws/src
$ catkin_create_pkg battery_simulator actionlib std_msgs

Now, let's go into our workspace and create a folder called action:

$ cd ~/chapter_4_ws/src/battery_simulator/
$ mkdir action

The action folder is where we will define our action file in the next step.