Dear Trongluan,
A Doctor said to his Patient:
"I want u to turn over onto your tummy".
The Doctor is examining the Patient. The Patient is lying on his/her back, face upwards, looking up at the ceiling. The Doctor says:
"I want you to turn over onto your tummy".
This means:
"I want you to turn your body over, onto your stomach, so that you are lying on your stomach, face downwards, looking down at the floor".
The word �tummy� is an informal word for the �stomach �, the �abdomen �, the �belly �, used by many English speakers.
Little children cannot say �stomach � very easily, so the Mam, (the Mother), uses the informal, affectionate, baby-word, �tummy�, �tum�, or �tum-tum�, and many speakers continue to use this word into adulthood.
The technical word for, �lying on the back, face upwards �, is �supine �; �lying on the stomach, face downwards �, is �prone �.
I hope that this helps.
Les
