The Aspect Ratio of your photo is the ratio of the width by the height. If you have a square image (Ratio 1:1) and want to show it all, choose a square print size. If your image is rectangular (Ratio 2:3) choose a rectangular image.
See below an overview of print size to ratio:
|5x5, 6x6, 8x8 & 12x12||1:1|
|6x4, 9x6, 12x8 & 18x12||3:2|
|8x6 & 16x12||4:3|
Cropping is the process of removing sections of the image from the edges, allowing you to reframe an image into a different aspect, focussing on a particular section of the image.
You can crop your image using the following process:
Having selected your desired print size, if it's apparent that not all of the image is showing, then the image has a different aspect ratio from the print size selected. See below examples:
To correct this, please try selecting a different print size better suited to your image.