'When' and 'while' are both used to refer to moments in time but they are not always interchangeable.
As a general rule :
‘When’ means ‘at the time that’.
‘While’ means ‘during the time that’.

WHEN : We use 'when' for:
-short actions:

• I was in the garden when the postman arrived.
• We were surprised when someone knocked on the door.
• When Zoe turned up, people were beginning to leave.
• An ambulance was already there when the police arrived.
• When she left home, she forgot to lock the door.

-to refer to a specific point in time :

• When I was a child, we lived in a small town.
• I took my first driving lesson when I was sixteen.
• When we moved house, the children had to change schools.
• Barry and Stella met when they were students.
• When I lived in India, I got used to spicy food.

-'when' can replace ‘whenever’ meaning ‘every time’ :

• The children get all excited when we go camping.
• We always stay at the Royal Hotel when we’re in London.
• I get bored when I have nothing to do.
• Many people feel nervous when they have to speak in public.
• I pack the suitcase(s) when we go on holiday.

WHILE : We use ‘while’:
- to talk about continuous or ongoing actions :

• While I was mowing the lawn, the postman arrived.
• I often listen to music while I do my homework.
• The electricity went off while I was cooking dinner
• While you peel the potatoes, I'll chop the onions.
• Tom tidied the garage while the kids were playing outside.

- for contrast :

• While many Brits drink beer, the French prefer wine.
• While I don’t agree with you, I understand your point of view.
• While Jeff is very sociable, his wife is more reserved
• While it had seemed impossible, a peace agreement was signed.
• While we enjoyed our trip, we were glad to come home.

- as a noun meaning ‘some time’ :

• We haven't had any rain for a while.
• It's been a while since I last spoke to Alice.
• It might take a while to repair this.
• It took a while for me to remember the title of the book.
• The nurse said she would be back in a little while.

Sometimes either 'when' or 'while' can be used:

• Jack arrived when/while we were having dinner.
• The boss came in when/while I was dealing with a customer.

*The word ‘whilst’ can replace ‘while’, but it is a little old-fashioned and less frequently used.

*The verb 'to while away' means to spend or pass the time the time doing something pleasant.
- We whiled away the time playing board games.
- The old man whiled away the afternoon doing crosswords.