Resizing and cropping are different operations, and confusing them is why people lose part of an image they meant to keep.
Resizing scales the whole image and keeps everything in frame. Cropping removes part of it. If you demand an exact width and an exact height that do not match the original proportions, something has to give, and it is either cropping or stretching.
Stretching is the worse of the two. A squashed or elongated photograph looks wrong immediately even to people who cannot say why, and faces give it away fastest.
If you genuinely need exact dimensions in both directions, crop to the right shape first and then resize. That way you choose what leaves the frame instead of a tool choosing for you.
Because the size you asked for is a different shape from the original. Something must be removed or stretched to fit.
You can, but enlarging cannot add detail that was never captured.
No.