When you know the degree and use it with cosine, you get the x-coordination on the unit circle (a circle with a radius of 1)
Using the degree with sine, you will get the y-coordination on the unit circle.
Let us put a dot on the unit circle with 30 degree.
Calculating cos(30) gives us 0.866
We can check this visually. Draw a vertical line from the dot and read the point where it cross the x-axis.
Same can be done for sine
Calculate sine(30) gives us 0.5
Check this visually by drawing a horizontal line from the dot. Read the point where this line cross the y-axis.
Try this for zero degree and 90 degree.
You will see cos(0)=1 and sin(90)=1 ,so cos(0)=sin(90)
Hopefully it helps!