What editing software are you using and what size do you want to print?
The problem is that photos are rectangles and rectangles come in different shapes, not just different sizes. Some are tall and skinny and others are short and fat (no comment which category I fall into). The shape of the rectangle that comes out of your camera may or may not match the shape of the photo you want to print.
The shape of the rectangle is measured in terms of the ratio of the long side to the short side. So a 4x6 print has a ratio of 1.5 (6 divided by 4 = 1.5) but a 5x7 has a ratio of 1.4 (7/5=1.4). So if you have a picture file and want to print it as both a 4x6 and a 5x7, something will have to be cut off because your 4x6 is more tall and skinny, while the 5x7 is more short and fat. And an 8x10 with a ratio of 1.25 would be shorter and fatter still, cutting even more off your photo.
Some photo editing programs have an option within the crop tool where you can tell it what size you want to print. Then the crop box will have the proper ratio you need. If your software does not have that, it should tell you how large your photo is in pixles. If you crop your photo so that it is 1,800 pixles wide, you would need to make it 2,700 pixles tall to get a 4x6 print and 2,520 tall to get a 5x7 and only 2,250 tall to get an 8x10. Your actual pixels will vary, but as long as you get the ratio right, your photos should come out just fine.
