A good animated example
You need to be familiar with how to find a side and how to find an angle using the cosine rule
1. When all three sides of a triangle are known or can be calculated. In this situation, the Cosine Rule can be used to find any and all of the three angles
2. When two sides are known, and the included angle is either known or can be calculated (e.g. using the other two angles). In such a situation, the length of the third side can be calculated, and so can the other angles.
3. If two sides and an angle besides the included angle is known, the Cosine Rule can still be used, but the Sine Rule is easier to use.