Resizing and cropping are different operations, and confusing them is why people lose part of an image they meant to keep.
Keep the shape lock on to retain the whole image in proportion. This tool does not add padding to fill a fixed canvas without stretching. A padded layout needs a separate editor.
Locked resizing keeps each image's proportions. Fixed dimensions can stretch images; crop to the required ratio first.
The encoder creates a new file. Upscaling cannot recover detail that the original did not contain.
With Keep the original shape switched on, you set only the width and the height follows. Nothing is cut off, because the tool resizes and does not crop. The proportions stay exactly as they were, so nothing looks stretched.
If you have a box to fit, say 800 by 600, a picture of a different shape will not fill it exactly. Set the width that makes the height fit, or accept that one dimension will be smaller. Making a picture smaller keeps it sharp, while making it larger softens it.
No. Check dimensions here, then use Compress to a size if the destination separately limits file size.
JPG, PNG and WebP always open. Other types depend on your browser, so convert them first with Convert format. A very large photo can run out of memory on a phone, so try a computer.
Making it smaller keeps it sharp. Making it larger cannot add detail, so an enlarged picture looks softer.