A modern, high-performance sailplane will move forward approximately 50 feet for every foot it descends. But even though the angle of descent is very shallow, the plane is still moving downwards. It's just like when you're walking down a stairway - no matter how shallow the slope is, eventually you will reach the first floor. Fortunately there is more to soaring than just a slow, steady descent.
Sailplanes can keep flying for hours and hours and can sometimes even outclimb powered planes.
The only way to achieve this is to use upward moving winds - what glider pilots call lift . But it's easy to realize that the air can also move upwards and downwards. If a sailplane flies inside of a block of rising air, the plane will climb together with the air. It's just like walking downward on an upward-moving escalator. Even though you're essentially walking down, you may be in fact be moving upward, if the speed of the escalator is greater than your walking speed.