This page uses the IDEE WMS servers to display 'slippy maps' of rasterised Spanish IGN maps, the 1:50,000 ones and the overview maps showing relief. At certain times of the day, these servers are currently rather slow. At the more detailed zoom levels, you can change the display to the Plan Nacional de Ortofotografía Aérea aerial photography by clicking the + top right and selecting that layer (at lower zoom levels, it displays poorer-quality IGN rasters). If you just see a pink screen, the servers are probably out of action - try again some other time.
You can zoom in/out using the controls on the left, or pan the map by dragging it (hence 'slippy map'). If you double-click, it will zoom in and centre on the point clicked. You can also shift/drag to zoom into the highlighted area. You can if you wish resize the window.
You can search for a lat/long coordinate by clicking on the search icon and entering the coordinate. This will create a marker and recentre the map at that coordinate. You can delete these markers by clicking the erase icon. I will add a placename search once I've worked out how to do that :-)
'Permalink' enables you to keep a particular view (coord/zoom level combination) for future reference, by storing it, adding it to your bookmarks, emailing it, etc.