Hi @rt.indru,
Welcome to the Community.
You are already on the way to solving the problem, based on the related forum post you found. This post specifically states what the problem was. The problem must have been this part:
Could you do the following:
echo $ROS_PACKAGE_PATH
You should get this path:
/home/user/catkin_ws/src:/home/simulations/public_sim_ws/src:/opt/ros/kinetic/share
This allows the ros system to find all the packages.
In any case, this problem is likely to be fixed by the time you come back to the course. If it isn’t then please check the post mentioned above and try again.