The zero conditional is used to describe things that are always true, regardless of specific conditions. It consists of an "if" clause describing a condition followed by a main clause describing the result. The condition and result use the simple present tense. Some examples of zero conditional sentences include: "If you heat water to 100 degrees, it boils" (describing a scientific fact), "If it rains, the grass gets wet" (describing a generally true outcome), and "Wood doesn't burn if there is no air" (another scientific fact).