If you’re dealing with rotation, you’ll want to be familiar with angles! Angles are measured in degrees, with 0° being to the right, increasing counter-clockwise. 90° is at the top, 180° is to the left, and 270° is at the bottom. A full rotation is 360°.
Angles can also be less than 0 or more than 360. It just keeps going around in the circle, though, so something like -90° is the same angle as 270°.
Angles are an important measurement, so you should be as comfortable with them as possible.