How does the sine rule work, and when is the cosine rule used?

When using the sine rule all the angles and sides are labelled A, B and C, and a,b, and c, in which every angle is opposite to its side – of a, b, and c. And it is used when one pair of an angle and side are known e.g. A and a, but only half of another is known e.g. B, to find the other half of b. While the cosine rule is used to find an angle when all three sides are known or when two sides and their included angle is known.