WHILE CRUISING ON A SCHEDULED CARGO FLIGHT IN IMC THE PILOT ENCOUNTERED MODERATE TO SEVERE TURBULENCE NEAR AN AREA WHERE WEATHER CELLS COULD HAVE BEEN OBSERVED ON THE AIRCRAFT'S RADAR. THE PILOT REVERSED COURSE, DECLARED AN EMERGENCY AND LOST CONTROL OF THE AIRCRAFT. THE AIRCRAFT ENTERED AN UNCONTROLLED DESCENT, COLLIDED WITH TERRAIN AND WAS DESTROYED.THE RECENTLY HIRED PILOT HAD COMPLETED THE FAA APPROVED GROUND AND FLIGHT TRAINING PROGRAM IN THE AIRCRAFT. DURING THE PILOT'S RECENT TRAINING, NEITHER THE FAA NOR THE OPERATOR REQUIRED THE PILOT TO DEMONSTRATE PROFICIENCY IN UNUSUAL ATTITUDE RECOVERIES OR HAVE KNOWLEDGE IN THE OPERATION OF THE AIRCRAFT'S WEATHER RADAR. COMPANY EMPLOYEES, WHICH INCLUDED THE PILOT'S HUSBAND, STATED THAT THE PILOT HAD NO PREVIOUS EXPERIENCE WITH WEATHER RADAR AND DID NOT UNDERSTANDTHE WEATHER RADAR INSTALLED IN THIS AIRCRAFT. THEY FURTHER STATED THAT THE PILOT APPEARED TO BE TIRED.