Use 'when' to ask or talk about time. It helps to know the exact time something happens. It is a question word.
When do you go to school?
When did she call you yesterday?
'When' connects two ideas about time. It shows one thing happens at the same time as another. It is a common joining word.
Call me when you arrive home.
When he speaks, everyone listens.
'When' can mean the exact time or moment something happens. It can be a noun to talk about time as a fact or point.
I remember the when of our meeting.
The when of the event is unknown.
'When' can show an uncertain time or condition. It introduces reported questions or uncertain situations in sentences.
I don’t know when she will be back.
Tell me when the class starts.
Used to ask with irony or doubt about the timing or frequency of something, often to make a critical point.
When will you ever learn?
When was the last time you helped?
'When' can talk about a time in the past during which another event happened. It shows background or context.
She was young when she moved here.
They lived in London when it rained a lot.
'When' links a time phrase that gives more information about the main action. It works like a relative adverb.
I met her when I was in college.
The phone rang when you left.
