At the end of an Apollo flight, the Command Module (CM) is turned around 180 degrees just prior to re-entering Earth's atmosphere. This is in order to:
a. Make sure that the Lunar Module (LM) will not burn up in the Earth's atmosphere
b. Ensure the ablation (heat) shield is the leading surface when the CM hits the atmosphere
c. Point the Service Module (SM) nozzle forward to make a slowdown burn
d. Allow the astronauts to eject and parachute out of the CM for the final descent