More detailed tutorial:
https://docs.ros.org/indigo/api/moveit_tutorials/html/doc/ros_visualization/visualization_tutorial.html
In the “Planning” tab of the “Motion Planning” subwindow, set the "Select Start State" field to “current”. Then click the "Update" button.
Use the marker (which are attached to the tip link of the arm) to drag the arm to a desired goal state.
After setting the start state and goal state, wait for around 5 seconds, then press the "Plan" button. You should be able to see a visualization of the arm moving.
Press the "Execute" button, robot will move as planned. In this process, you can press the "Stop" button to make the robot stop.