Three ways to resize
Keep proportions
Enter a width and height and every image is scaled to fit inside that box without being stretched. Portrait and landscape photos in the same batch each keep their own shape.
Exact size
Unlink the proportions to get exactly the size you typed. Choose Crop to fill to trim the edges, Fit inside to add a white, black or transparent background, or Stretch.
Percentage
Scale every image by the same amount, such as 50% to halve both sides.