Learner's definition of WHETHER
if it is or was true that
if it is or was better
— used to indicate choices or possibilities
Whether we succeed or fail, we must try.
It doesn't matter whether you pay by cash or check.
We're going whether or not you decide to come along. = Whether or not you decide to come along, we're going. [=we're going if you decide to come with us and we're going if you decide not to come with us]
I had to decide whether or not to respond to his letter.
The police are investigating whether (or not) the death was a homicide.
The game will be played whether it rains or not.