0 used to say that a particular thing can or will happen only after something else happens or becomes true: --
If disturbed, the bird may abandon the nest, leaving the chicks to die.
I wouldn't work for them (even) if they paid me twice my current salary.
If she hadn't called, I wouldn't have known.
If anyone calls, just say I'll be back in the office at four o'clock.
We'll have the party in the garden if the weather's good. If not (= if the weather is not good), it'll have to be inside.
1 used to introduce a clause, often in indirect speech, that shows two or more possibilities: --
4 used to say that a particular thing can or will happen when, only when, or after something else happens or becomes true: --
5 (used to introduce a clause, often when reporting what someone else said) whether: --
I couldn't find the station, so I asked someone if they could direct me.
Biscuits will stay crisp if you keep them in an airtight container.
Try to act confidently, even if you feel nervous.