"If Clauses," also known as conditional sentences, express a condition and its possible outcome. They typically consist of two parts: the "if" clause, which states the condition, and the main clause, which describes the result. For example, in the sentence "If it rains, we will stay indoors," the condition is it rains, and the result is we will stay indoors. There are different types of "If Clauses," including zero, first, second, and third conditionals. The zero conditional describes general truths, while the first conditional talks about real future possibilities. The second conditional refers to hypothetical situations, and the third conditional discusses past events that did not happen.