Installing the OS (Ubuntu)
ROS 2 works on three OSs: Ubuntu, Windows, and macOS. Although Ubuntu and Windows get Tier 1 support, macOS has only Tier 3 support, meaning “best effort,” not “fully tested.” You can learn more about what Tier 1, 2, and 3 mean on the REP 2000, which describes the timeline and target platforms for ROS 2 releases: https://www.ros.org/reps/rep-2000.html.
This means that using macOS for ROS 2 is not necessarily the best choice for learning (if you’re an Apple user). We’re left with Windows or Ubuntu.
From teaching experience, I saw that even if ROS could work well on Windows, it’s not easy to install and use it correctly. Lots of bugs can occur, especially with the 2D and 3D tools. When you’re learning ROS, you want a smooth experience, and you want to spend time learning the features, not fixing the configuration.
Hence, the best overall option is to use Ubuntu. If you don’t have Ubuntu...