Here are some instructions to follow the hands-on demo.

xhost +

disables access control on your XServer. Maybe needed if you don't see a Gazebo Windows opening.

Press the "Use template" button on the top right.

This moves the repo to your own namespace without the commit history. You can now clone the repository.

Now open the cloned repository with VSCode. While opening it will propose to open the folder in a remote container. Press the button "Reopen in container" and Code will build the container environment.

You may need to remove "--gpus=all" from the devcotainer.json file if you don't have a Nvidia GPU, since this is a nvidia-runtime2 specific option.

Now build the clone the turtlebot3_gazebo repository using the following command:

vcs import < src/ros2.repos src

After completing this task, you can build the packages:

colcon build --symlink-install

And now source the ROS2 environment:

source install/setup.bash

Now you can run the demo by first starting a simulation:

ros2 launch turtlebot3_gazebo turtlebot3_house.launch.py

and in another terminal, which you can open with the little split button:

ros2 run turtlebot3_teleop teleop_keyboard