Problems after installation

After I install the "turnbot_simulator", whenever I open a new terminal, I will report:
[rospack] Error: package 'turtlebot_gazebo' not found
[rospack] Error: package 'turtlebot_gazebo' not found
[rospack] Error: package 'turtlebot_stage' not found
[rospack] Error: package 'turtlebot_stage' not found
[rospack] Error: package 'turtlebot_stdr' not found

How to solve that problem?