where is the first place what must see in Vienna?

By merakli01where they make the sausage
The best place I saw in Vienna was the city center called Kratzplatz or something like this; it is very nice, you will like it. It is almost old Vienna, untouched. You know you can find it through subway info points, they call it Uban. And believe me that people in Vienna are really nice as they answer to your questions very easily in English, they just feel themselves committed to answer. Have fun my boy and send us photos...
He was referring to Karlsplatz, but personally I'd recommend St. Stephen's Cathedral, then walk up the "Kärntner Straße" to the opera house.