0 used to say that a particular thing can or will happen only after something else happens or becomes true: --
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.
If anyone calls, just say I'll be back in the office at four o'clock.
If she hadn't called, I wouldn't have known.
I wouldn't work for them (even) if they paid me twice my current salary.
If disturbed, the bird may abandon the nest, leaving the chicks to die.
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: --
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
We kunnen het stap voor stap voltooien, hoe lang de weg ook is en het kan niet worden voltooid, hoe kort de weg ook is, als je niet eens je voetafdruk markeert.