You just came back with a camera full of new images. Some of them are landscape, some portrait and those need to be rotated for viewing on the computer. There are two ways to do that with Photo Gadget Pro.
Automatic rotation based on EXIF
If your camera stores the information about image orientation in the image file itself using EXIF then you can simply select all images, right click the selection, choose "Based on EXIF" option and click Rotate. Photo Gadget Pro will then rotate only images that really need to be rotated and skip the rest.