Once you have a VM you should be able to connect to it via ssh:

<os>@hostname.vsos.ethz.ch where os is usually “debian” or “ubuntu”

Remember to connect via the right sshkeys i.e. if you are using else than the standard one use -i path/to/your_key or add it to your ssh config

You also have the option for troubleshooting to connect to <your-hostname>@sshportal.sos.ethz.ch. For details, see sshportal documentation. There again use the keys that have been setup with your VM.

In your VM you can obviously just add keys to be able to connect with different keys (for example for different machines or if you want to give access to other people) To be able to use the shell from sshportal you need to add those keys by connecting to it and using the tool to add them.