Trigonometry deals with the relationship between the sides and angels of a specific angle. It also deals with the relevant functions of any angles.
Trigonometry in Right Triangles
In right triangles we have 3 trigonometry rations which can be applied to find either a missing side or a missing angle: Sine (sin) Cosine (cos) and Tangent (tan). An easy way to remember these ratios is using SOH CAH TOA. Each letter stands for a word which tells you what information to use. In SOH, S means Sine which equals O (opposite side) divided by H (hypotenuse). CAH means C for Cosine which equals A (adjacent side) over H (hypotenuse). Tangent does not use the hypotenuse and thus is T (tangent) equals O (opposite side) over A (adjacent side).
Trigonometry in Non-Right Angle Triangles
When we don't have a right angle available in a triangle but we need to find a side or an angle we use the Sine Law and the Cosine Law (not to be confused with Sin & Cos). These trigonometric functions are somewhat more difficult and use a more complicated formula.