It’s a helpful way to visualize basic trigonometric functions.
For the rest of this guide, we will be using radian notation, instead of the standard degree one you may be familiar with.
As a reminder, any degree can be expressed in terms of a radian, with the core ratio being that 180 degrees is equal to π radians. With this, you can establish that 60 degrees is π/3 radians, 45 is π/4 radians, ect.
You may already know that the y-values on a point on the unit circle represent cosine and the x-values represent sine, but it is important to build an intuition of why this is for calculus. Later topics require you to have a solid grasp on trigonometry to solve all kinds of problems.