Quaternion is a structure that is good at representing the 3D rotations of object in all axes at once.
It's better then Euler angles representation, because of few things:
- it gives natural and smooth interpolation (animation), from one quaternion-based rotation to another,
- it does not suffer from gimbal lock.
If you want to use Euler angles instead
At the same time, framework will still use quaternions "under the mask" (so you will get all the benefits, including smooth interpolations).
Better understanding of Quaternion
If you are interested in what Quaternions are in general, we suggest you to check the great explanation video made by thebennybox.