Sometimes the shape of the paper is not the same shape as the actual photo. For example, a square is always a square even if it’s printed at 4×4 or 8×8. Rectangles have specific shapes too, but it’s not always so obvious to see. (The fancy name for this is “aspect ratio” or in other words it’s width by height.) Rectangles can be short and fat or long and narrow, and anywhere in between! And this means that our photo might need to be cropped depending on the paper shape we are going to print on.
If you don’t want to lose any of your image: Choose any print size that is a 3:2 ratio (the same as the camera). That will keep the whole image intact without any cropping.