Customization

I’d like to add one more point regarding images.
I noticed they are all in the same size ratio.
A.
Are they cropped after upload, automatically, or uploaded with that same size ratio?
B.
How would they look if they are being uploaded all in different size ratios?
C.
Can the system allocate different thumbnail sizes, depending which thumbnail is being displayed (but that would then again need to be through cropping, too, to avoid image distortion).

Sorry if I’m a pain in the neck. Just trying to find out, especially since I am new to WP.

Thanks for your understanding.