You're reading the documentation for a version of ROS 2 that has reached its EOL (end-of-life), and is no longer officially supported. If you want up-to-date information, please have a look at Galactic.

Guides

Guides provide direct and modular answers to “How-to” questions regarding key aspects of ROS 2. They contain succinct steps to help you accomplish important tasks quickly.

Guides are meant for users who already have some knowledge of ROS 2 and just want to find out how to implement something specific. They will not go in-depth by providing background information or teaching how a concept ties into the greater ROS 2 ecosystem.

If you are new and looking to learn the ropes, start with the Tutorials for a more well-rounded progression through ROS 2.