Q: How do I leave from Cyrodiil?
Though Cyrodiil has a fast-travel system with waypoints / wayshrines, it’s not connected with any areas outside Cyrodiil.
To leave Cyrodiil you will need to visit the starting area of your faction. Only there can you interact with a wayshrine which can take you outside of this zone. The map below shows the locations of wayshrines that can teleport you outside of Cyrodiil: