First open a terminal window, move to robotics folder, source the devel/setup.bash and start the gazebo simulation
cd roboticssource devel/setup.bashroslaunch open_manipulator_gazebo open_manipulator_gazebo.launchStart the simulation by pressing the "play" button in the lower part of the screen.
Then open another terminal window, move to robotics folder, source the devel/setup.bash and start the gazebo controller
cd roboticssource devel/setup.bashroslaunch open_manipulator_controller open_manipulator_controller.launch use_platform:=falseThen open a third terminal window, move to robotics folder, source the devel/setup.bash and start the gazebo controller
cd roboticssource devel/setup.bashroslaunch open_manipulator_control_gui open_manipulator_control_gui.launch