Why don't you look them up in the dictionary such as “朗文当代高级英语词典（双解版）or “麦克米伦高阶英汉双解词典” ? Then you can find the answer about the difference between "if" and "whether"(not wether). Just do it !

在此只说主要区别，不说两者通用的部分。

1，在不定式前面只能用whether。She can't decide whether to marry him.
2，在介词后面只能用whether。There are doubts about whether the system is safe.
3，在后面紧接“or not”时只能用whether。The question is whether or not the government has the right to interfere.

one thing i know about using 'IF' is when your sentence is conditional, and 'WHETHER' is when you express a doubt / question or when you use two alternatives.

ex1: I will only attend the party IF you will promise not to spoil it.
ex2: She's thinking about spending her money on WHETHER she will travel abroad or buy a new car.

so to speak, "if" is usually used for 1 conditional sentences like "I wouldn't do that If i were you" but "whether" is usually used for 2 conditional sentences that you want to express a sentence about two different possibilities like "I haven't decided yet whether to stay or leave"

sometimes "whether" can replace "if", for example "She asked me whether I wanted to go to the party tonight" or "She asked me if I wanted to go to the party tonight"

also you have to use "whether" after prepositions like "it depends on whether it's sunny or not"

hope you got ur answer