Trigonometry is about right-angled triangles (90°). There are names for each side of the triangle: The hypotenuse, opposite and adjacent. the angle between the hypotenuse and adjacent is called theta.

The 3 functions of trigonometry are:
Sine, Cosine and Tangent (Sin, Cos, Tan)

There is a word to remember how the functions work: Sohcahtoa