Graham:
You need to learn a little more math. Start here:
https://www.mathwarehouse.com/geometry/triangles/right-triangle.html The problems are easy.
Then look at "special right triangles":
https://www.mathwarehouse.com/geometry/triangles/right-triangles/special-right-triangles.php
If you can get through that without issues, then look at ONLY sine, cosine and tangent here:
https://www.mathwarehouse.com/trigonometry/
ASK questions.
What was a killer for me is that when taking Calculus, I had to MEMORIZE nearly all of the special angles and values such as 0, 30, 45, 90 and multiples up to 360 degrees. They all generally can be derived from the unit triangle where one side is 1, 1, and √2 in length. The other can be derived from lengths 1, 2 and √3 and knowing that "Oscar Had A Headache over Algebra". Sin = O/H, Cos = A/H and Tan = O/A. The term "O" means opposite; H= Hypotenuse and A= adjacent.
Once you know what sine, cos and tangent which is sin(θ)/cos(θ), then there are 1/sin, 1/cos and 1/tan which are also given special function names of secant, cosecant and cotangent.
The real value of the basic information is to be able to find any side or any angle of a right triangle given 3 pieces of information, a mix or match of side lengths and angles.
Just concentrate primarily on the sine and cosine and tangent. It should be easy.
The sine function has a value of 0 at 0 degrees and a minimum value of -1 and a max value of +1. The cosine function has a value of 1 at 0 degrees. As you can see here:
https://www.wolframalpha.com/input/?i=sin(x);+cos(x) , cos function is just a phase shifted form of the sine function PHASE SHIFTED. See
https://www.wolframalpha.com/input/?i=sin(x+pi/2),+cos(x)
Let's hope you can make some sense out of all of this. It's an important concept to grasp.
when we are all done, I hope you would understand that two equations of a circle are:
X^2 + Y^2 = R^2
and x=sin(θ); y = cos(θ)
are equations of a circle with a radius of r The second equation is known as the parametric form where θ is the parameter. The first is known as the Cartesian form or a set of X,Y pairs.
Your not there yet, but that's where we are heading.