WHEN / WHILE

✔WHEN:    use the past simple

WHEN HE WAS  AT HOME , THE PHONE AS RINGING

 EXAMPLE:

-She was surfing when the shark.

-I was having a picnic when I saw my sister.

-When you called ,he was watching TV.

✔WHILE:  use the past progressive 

HE WAS AT HOME, WHILE THE PHONE AS RINGING

 EXAMPLE:

-While he was calling, her friend arrived his house.

-While they weresearching the forest,the police noticedsomething.

-While she was having lunch, he saw a pig.