Open session3_cliserver/CMakeLists.txt and add following lines to the bottom of the file.
add_executable(server src/server.cpp)
target_link_libraries(server ${catkin_LIBRARIES})
add_dependencies(server session3_cliserver_generate_messages_cpp)
add_executable(client src/client.cpp)
target_link_libraries(client ${catkin_LIBRARIES})
add_dependencies(client session3_cliserver_generate_messages_cpp)
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 session3_cliserver server
Open a 3rd terminal in the workspace root and run,
source devel/setup.bash
rosrun session3_cliserver client