I remember we had that at maths and I studied it as much as I could in class, but since I had no use for it for all these years, I've pretty much forgotten about it.

And I still dont get how would one use trigonometry in CC. What is it for?

Triangles, broseph, triangles.

You can do more with triangles than you ever thought possible.

To get the X and Y components of vectors from their direction angle and magnitude? That's pretty much it. I think all my mods that use lua have trigonometry involved in some form though.

a is the direction angle, a and b are the X and Y components and c is the magnitude.
a = (cos a) * c
b = (sin a) * c
c = square root of (a^2 + b^2)

Fiddling with this can cause stuff such as vortex guns.