Hello !
To find the sine,cosine,tangent for a point on a circle,it is mandatory to trace the point projections on coordinate axes.
For example,if you have a point A on the circle,the projection on the x-axis may be A₂ ,and the projection on the y-axis may be A₁ .
OA₁ - the length from the center of the circle (O) to the y-axis projection
OA₂ - the length from the center of the circle to the x-axis projection
The hypotenuse (AO) is √(AA₁² + AA₂²)
Now,the formulas :
sin θ = AA₂/OA
cos θ = AA₁/OA
tan θ = AA₂/OA₂
cot θ = AA₁/AA₂
You have a drawing below,I hope you will understand :)
Have a nice day !