A Web Map Service (WMS) is a standard protocol for serving georeferenced map images over the Internet that are generated by a map server using data from a GIS database.
Choose WMS - Web Map Service from Background Map menu.
Add a WMS Server and click Connect.
Choose a WMS Layer from the list and Add Selected Layer as WMS Layer (online) or Add Selected Layer as background maps (offline).
Close the dialog box. You can manage the view by choosing Manage from the Background Map menu.
One possibility to display the map: