I'm going to use a photo from a recent trip. Not the greatest photo, but it will make a good example. What do you see when you look at the photo? Some people dab smack in the middle of a bunch of trees. Not the greatest composition. Maybe you'd like to have a photo that really has the family as the subject and a bit closer so you can see their faces. This would be a time that you would use cropping. The crop tool is used when you want to change the composition of your photo.
Start by selecting your crop tool. It's the one that looks like a weird square.
There are settings that you can set up on your tool. They differ in Elements and the full Photoshop versions. In Elements you can select to use the “Aspect Ratio: Use Photo Ratio.” setting. This will keep the relationship between the height and width of your photo the same as it was when it came off the camera. Most cameras produce images that will print at 4x6 ratios. In the full version of Photoshop you can select the "crop 4in x 6in" option from the tool drop down. Be sure to keep the dpi setting the same as your original photo.
Click and drag it over your photo. You'll see the area that is selected will be lighter than the rest of your photo. Release the mouse when you have selected the area that you want to keep. You can move it about to relocate it on your photo. When you are happy with the selection, press the check mark to crop your photo.
This is my cropped photo. Notice how the composition has been changed? The sign post and most of the trees around the peripheral are no longer in the photo. The subject of the photo is now the family gathered on the bench.
Remember when you save your cropped photo to choose File > Save As, and give it a new name. This way you will not overwrite your original file and can retain it for future use.
Hope you enjoy this little tip to help you get the most out of your photos!