The bus system in Paris is complex. First, you need THE Book, on where the busses go and what the numbers mean.  That book is "Le petit Parisien, 3 plans par arrondissement” – found around Paris in lots of places – and even on the web in some travel shops.  It is worth getting before you head off – nice reading on the plane, so you can plot your journey around Paris, above ground.  It has the Metro lines in it too – and actually great resolution of the whole of Paris.  For each arrondissement it has a street map, a bus map and a metro map – transportation is so dense in Paris, you can not put all three on the same page.  It has the taxi stands also tucked in there with the various daily markets of Paris.  This is truly the book that helps you get around Paris and see the city…