Conditionals are sentences that express the result of a certain situation or condition. They consist of an "if" clause (expressing the condition) and a main clause (expressing the result). There are different types of conditionals, including zero, first, second, and third conditionals, each used to talk about different types of conditions and their possible results. We use conditionals to talk about hypothetical situations, things that are possible, or things that could have happened but didn't. They help us to express ideas about cause and effect, and to imagine different outcomes based on different conditions.