ROS is the Robot Operating System. Its really helpful for everyone who doesn’t want to reinvent the wheel when it comes to robotics.

In my opinion its a bit hard to have a start, and its easy to get confused because of the changes they did between multiple ROS versions.

Some  stuff I can recommend:

• ROS Wiki
• ROS Cheat Sheet for Hydro PDF made by clearpathrobotics
• ‘A Gentle Introduction to ROS’ by Jason M. O’Kane PDF Website
• ‘Learning ROS for Robotics Programming’ by Aaron Martinez and Enrique Fernandez

Promising but not yet read:

• ‘ROS by Example’ by R. Patrick Goebel Website