Let's create and build a catkin workspace:
$ mkdir -p ~/catkin_ws/src $ cd ~/catkin_ws/ $ catkin_make
The catkin_make command is a convenience tool for working with catkin workspaces. Running it the first time in your workspace, it will create a CMakeLists.txt link in your 'src' folder. Note, for Arch Linux users, the first catkin_make command in a clean catkin workspace must be:
$ catkin_make -DPYTHON_EXECUTABLE=/usr/bin/python3 -DPYTHON_INCLUDE_DIR=/usr/include/python3.7m -DPYTHON_LIBRARY=/usr/lib/libpython3.7m.so
This will configure catkin_make with Python 3. You may then proceed to use just catkin_make for subsequent builds.
Additionally, if you look in your current directory you should now have a 'build' and 'devel' folder. Inside the 'devel' folder you can see that there are now several setup.*sh files. Sourcing any of these files will overlay this workspace on top of your environment. To understand more about this see the general catkin documentation: catkin. Before continuing source your new setup.*sh file:
$ source devel/setup.bash
To make sure your workspace is properly overlayed by the setup script, make sure ROS_PACKAGE_PATH environment variable includes the directory you're in.
$ echo $ROS_PACKAGE_PATH /home/youruser/catkin_ws/src:/opt/ros/kinetic/share