Vienna is divided into 23 districts. Most of the historical sites can be found in the central 1st district, "Innere Stadt", which is basically the area inside the "Ringstraße" (ring road). Among other sights, here you find the Hofburg, the Stephansdom, and Kunsthistorische Museum. All distances within the 1st district can be reached by foot in no more than 10-20 minutes.

Schönbrunn Palace is not located in the center of Vienna, but can be easily reached by the line U4 of the subway. It also pays off to take the public transport to go to the Belvedere Palace: you can take the tramway line D from the western part of the Ringstraße in the direction of the Südbahnhof.

City maps are available free of charge at tourist information offices (e.g. at Kärntnerstraße 38). There are also good maps on display at bus and tram stops and in the subway stations. You find maps of the subway system on the trains and at the stations: they are self-explanatory, not a word of German required!

For an interactive online map of the city of Vienna:
http://www.magwien.gv.at/english/map/