...
The network just created is currently isolated from the rest of the world. To give this network access to other networks, and the internet, we need to create a router. Navigate to "Network -> Routers" in the left menu, and click the "Create Router" button. Give the router a name, and select which external network this router should be connected to. This articles has an overview of the various external networks available.
When the router is created, click on its name to start configuring it. We need to add an interface to the router, so click the "Add Interface" button.
...