If is a subordinating conjunction. It is mainly used to introduce a condition that must exist before something else can happen.
- If you don’t work hard, you will fail.
- If she is late, we will have to go without her.
- If she doesn’t pay the fee, she will not be allowed to take the test.
If clauses may also introduce a situation that may happen or may be real.
- If you miss this opportunity, you will have to regret later.
If you want / like
This expression is used to suggest that somebody has the freedom to do what they want.
- She can join us if she wants / likes.
If so means ‘if this is true’.
- Do you like our lessons? If so, would you mind sharing them on your favorite bookmarking sites?
If can be used to introduce a situation that always produces the same result.
- If you heat ice, it melts.
- I always get a headache if I don’t sleep well.
Indirect yes / no questions
If is used to introduce indirect yes / no questions. Whether is also possible in this case.
‘Are you ready?’ Rani asked me.
Rani asked me if I was ready.
‘Do you like classical music?’ she asked.
She asked me if I liked classical music.
I still haven’t decided if I am moving to another city.