Open session4_action/CMakeLists.txt and add following lines to the bottom of the file.
add_executable(ac_server src/ac_server.cpp)
target_link_libraries(ac_server ${catkin_LIBRARIES})
add_dependencies(ac_server ${session4_action_EXPORTED_TARGETS})
add_executable(ac_client src/ac_client.cpp)
target_link_libraries(ac_client ${catkin_LIBRARIES})
add_dependencies(ac_client ${session4_action_EXPORTED_TARGETS})
Go to root of the workspace
cd ~/ros_workshop/
catkin build
or
catkin_make
Open a terminal and run,
roscore
Open a 2nd terminal in the workspace root and run,
source devel/setup.bash
rosrun session4_action ac_server
Open a 3rd terminal in the workspace root and run,
source devel/setup.bash
rosrun session4_action ac_client