From BBC News:
To return to Earth the space shuttle must make a series of complicated manouevres to align itself into the correct position to achieve a safe descent.
1. The shuttle flies upside down in orbit to control its heating.
2. To re-enter the atmosphere, the shuttle is turned tail first to the direction of travel, and fires its engines to slow its speed.
3. The orbiter is then flipped the right way up and enters the top layer of the atmosphere at about a 40-degree angle from horizontal with its wings level.4. The orientation keeps its black thermal tiles facing the majority of the heat – as high 1,650C (3,000F) on the leading edges of the wings and nose.
5. As its speed drops, the shuttle starts to fly more like an aircraft, using its rudder and wing flaps for control. It banks sharply to slow its speed still further
6. The shuttle falls from a height of more than 360km at speeds that top Mach 30, and at an angle of 19 degrees, far steeper than that of a commercial aircraft. The spacecraft comes to a dead stop half a world a way from where it began the descent.