General

Unity uses 3 rotation systems.

1. Euler Angers - rotation about x, y, z axis
2. Axis Angle - A normalized Vector3
3. Quaternions

// Convert from Quaternion to Euler:
Vector3 inEuler = quaternionRotation.eulerAngles;
 
// Convert Euler to Quaternion
Quaternion inQuaternion = Quaternion.Euler(inEuler);
 
// To Axis-Angle
Quaternion randomQuaternion = Random.rotation;
float angle;
Vector3 axis;
 
randomQuaternion.ToAngleAxis(out angle, out axis);