How does an aircraft descend without its nose pointing down?
A plane descends when it does not have enough thrust to maintain its altitude. A plane can descend with its nose pointed up or down so long as there is not enough thrust to maintain altitude. Altering the pitch of an aircraft is used to control airspeed: pitching up slows an aircraft down (and may cause a climb if done from a level attitude) and pitching down generally speeds up an aircraft (and causes a descent if done from a level attitude). So if you want to descend at a slow speed you reduce power and pitch the nose up. 

Since you want to land at a slow speed you will need to pitch up and slow the aircraft down while reducing power to descend nicely. This article covers it nicely in terms of flying an approach. It's also covered in this question.