To get the newsest version if you are in the devcontainer already, you can skip this step.
If you are in windows, go into wsl first.
To run the devcontainer, installed the Dev Containers Extension.
You must also install the devcontainer cli first. After installign the extension, use (View -> Command Pallete -> Dev Containers: Install devcontainer CLI) to install the devcontainer cli. You might have to restart your computer.
For how to open the container, follow the VSCode documentation.
You can edit the produced devcontainer file locally. To make modification remotely, see the ros-container repo.
Presuming that you have opened the container already, you can build the code by running colcon build and then running source install/setup.bash or replace bash with your shell. Then use the ros2 run <pkg_name> <executable_name> or ros2 launch <pkg_name> <launch_file_name> command to run your packages.