It's not city center but that doesn't mean anything. Every conveinience available and center is only a 5 minute bike ride. Enjoy the real Amsterdam
There's one proper bedroom with 2 persons bed. In a second room (now a big dressing room) I can put a 2-person mattress on the floor as additional room for one or two people. That's why it says three people in the discription
Just treat it as it would be your own place.