Learn French: Mon bureau est au deuxième étage. - My office is on the second floor.

In English, you say a room is 'on' a floor, but in French, it is 'at' a floor. Therefore, we use the preposition à. Because étage is masculine, à and le combine to form the contraction au.

Doesn't bureau usually mean 'desk'?

It means both 'desk' and 'office'! You can usually tell which one is meant from the context. While you could technically have a desk on the second floor, a sentence describing where something is located in a building is almost always talking about an 'office'.

Is the deuxième étage the exact same thing as the second floor in North America?

No, it is actually the third floor for Americans and Canadians! In France, the ground level is called the rez-de-chaussée. The first floor up is the premier étage, making the deuxième étage two flights of stairs up.

Could I say au second étage instead of au deuxième étage?

Yes, you absolutely can. Traditionally, second is used when a series stops at two (meaning it would be the top floor of a two-story building), while deuxième implies there is at least a third floor. However, in modern everyday French, they are used interchangeably.