They are used to introduce subordinate clauses and join them to principal clauses/
main clauses. There are three kinds of subordinating conjunctions:
A) Simple subordinating conjunctions:
after, although/though, as, because, before, if, however, once, since, than, that, till/until, unless, when, where, while, whether
He came after I had left.
B) Compound Subordinating conjunctions:
I. as far as, as long as, as soon as, so long as, so far as, in as much as, just as
She garlanded him as soon as he arrived.
ii. in that, so that, in order that, such that,
now that, provided (that), considering (that),
granting (that), on condition that
You can go for the trek provided you are well.
iii. as if, as though, in case
Take extra money in case you need it.
C) Correlative subordinates
if … then
as … as
no sooner ….than
hardly …. when
If I don’t return in an hour then call the police.
Note: Relative pronouns and Relative adverbs, too, can function as subordinate conjunctions:
Relative pronouns –
Relative adverbs – when/where/why/whenever/wherever