"Whether" is similar to "if". You can use them in the same way:

I'm trying to decide whether I should take my laptop.

I'm trying to decide if I should take my laptop.

You might choose to use "whether" instead of "if" just because of the sound. "Whether I" sounds easier to pronounce than "if I".

In written English, you should follow "whether" with "...or not":

I'm trying to decide whether I should take my laptop or not.

You can also use "...or not" in spoken English, but you should put it right after "whether":

I'm trying to decide whether or not to take my laptop.