Whether is a word that introduces a choice between two or more possibilities. When you say “I don't know whether to wear my red shirt or my blue shirt,” you're showing that you're considering options and haven't decided yet.

The word often appears in questions about uncertainty: “We're not sure whether it will rain tomorrow” means the rain might happen or it might not. Teachers use it when giving options: “Please let me know whether you want to present on Tuesday or Wednesday.” Scientists use it constantly: “The experiment will show whether the hypothesis is correct.”

Whether sometimes gets confused with weather (the atmospheric conditions outside), but they're completely different words.

You'll also hear the phrase whether or not, which emphasizes that something will happen regardless of the choice: “We're going to the beach whether or not it's sunny.” This version stresses that the plan is certain even if the conditions aren't ideal.