whether or if...

[creep0318]

hey every one, I would like to know when shuold I use wether and when if. I am a little confuse about that.

I don't know wether/if he's in.

wich should I use, thank you for your help.

 

[Merce2]

You use whether when you mention two possibilities, and if when you mention only one.
E.g.: I'll come with you whether you like it or not.