I have been working on robots from couple of years and after graduation I made a course that contains all the ROS essential you need to work using ROS.
This course is not just simulation Implementation on hardware as well I will be Using Cheap Robots (any one can buy) to be controlled by ROS , including raspberry PI , esp-8266 and 2 wheel plastic car with sensors
After this course you can work with ROS so easily and will start making your upcoming robotics projects powered with ROS.
packages used are
-rviz
-gazeebo
-turtlebot3
Find Course on this --> !LINK!