If you want to learn more about the differences betwwen ROS 1 and ROS 2, you can find more information on the links below:

• Thomas, D. Changes between ROS 1 and ROS 2.
• Gerkey, B. Why ROS 2.0?

If you want to start learning ROS 1, you can learn through the following resources：

• ROS Documentation (Tutorials)
• 5 methods for learning ROS: which one is for you?

If you want to start learning ROS 2, you can learn through the following resources：

• ROS 2 Wiki
• ROS 2 installation
• ROS 2 tutorials