Frequency: The word is one of the 700 most common words in English.
1.
You use ~ to ask questions about the time at which things happen.
When are you going home?...
When is the press conference?...
When were you in this house last?...
‘I’ll be there this afternoon.’—‘When?’
QUEST
2.
If something happens ~ something else is happening, the two things are happening at the same time.
When eating a whole cooked fish, you should never turn it over to get at the flesh on the other side...
Mustard is grown in the field ~ weeds are there, rather than ~ the growing crops are there.
CONJ
3.
You use ~ to introduce a clause in which you mention something which happens at some point during an activity, event, or situation.
When I met the Gills, I had been gardening for nearly ten years.
CONJ
4.
You use ~ to introduce a clause where you mention the circumstances under which the event in the main clause happened or will happen.
When he brought Imelda her drink she gave him a genuine, sweet smile of thanks...
I’ll start to think about it ~ I have to write my report.
CONJ
5.
You use ~ after certain words, especially verbs and adjectives, to introduce a clause where you mention the time at which something happens.
I asked him ~ he’d be back to pick me up...
I don’t know ~ the decision was made...
CONJ
6.
You use ~ to introduce a clause which specifies or refers to the time at which something happens.
He could remember a time ~ he had worked like that himself...
In 1973, ~ he lived in Rome, his sixteen-year-old son was kidnapped.
PRON
7.
You use ~ to introduce the reason for an opinion, comment, or question.
How can I love myself ~ I look like this?...
CONJ
8.
You use ~ in order to introduce a fact or comment which makes the other part of the sentence rather surprising or unlikely.
Our mothers sat us down to read and paint, ~ all we really wanted to do was to make a mess...
= although
CONJ