Open a terminal and run,
roscore
Open a 2nd terminal in the workspace root and run,
source devel/setup.bash
rosrun session3_pubsub publisher
Open a 3rd terminal in the workspace root and run,
source devel/setup.bash
rosrun session3_pubsub subscriber
Open a 4th terminal in the workspace root and run,
source devel/setup.bash
rosrun session3_pubsub publisher
Open a terminal and run,
roscore
Open a 2nd terminal in the workspace root and run,
source devel/setup.bash
rosrun session3_pubsub publisher __name:=publisher1
Open a 3rd terminal in the workspace root and run,
source devel/setup.bash
rosrun session3_pubsub subscriber
Open a 4th terminal in the workspace root and run,
source devel/setup.bash
rosrun session3_pubsub publisher __name:=publisher2