Add the URL to your resource and the Type in the lower left part of the dialog titled "Add New Resource"
Click on the "Add" bottom at the bottom right corner of the "Add New Resource" panel
The resource is added to the "Resources" list.
Explore the resource (click on the button to expand datasources)
Select a layer for visualisation. The details, if any are available, are shown in the right hand side of the "Add Resource" dialog.
Click "Next" in the bottom right corner of the "Add Resource" dialog.
Select whether to add the map to an existing map view or to a new one. If you want to define a new map view you can also choose the projection (server support required!). Then click "Add to Map".