Screen console: Under Manage → Screen console you can see your server's screen in the browser, even if the network or SSH no longer works (e.g. after a wrong firewall rule).
Rescue system: Switch it on and restart the server. It then boots into a Linux rescue system instead of from the disk – so you can recover files or repair settings. The password for it is listed under “Access”. Afterwards, switch the rescue system off again and restart.