Cropping an image mean selecting a portion of the image to work with. This tool is used when we have some extra (un-useable) area of the image. For example, we scan the document and it is scanned with some extra black area or white area, which is not the part of the image. We can use crop tool to remove this extra area.
We can use this tool by two methods. First select the crop tool from main tool box or Press C. The tool will be selected. Now, selected the area that you want to keep and press Enter, the area outside the selected area will be deleted. Second way is the select the area by using the rectangular marquee tool. Make a selection and from menu bar select Image -> Crop. This will give you the same result.
To rotate an image, we have also two methods. First is to use the free transform tool, to use this Press Ctrl + T or from menu bar Edit -> Free transform. The layer should be unlocked to use this tool. A rectangle box will be shown with boxes at corners and middle. Using these boxes we can rotate or resize the image.
The second way is to use the Image –> Rotate Canvas -> Arbitrary/180/90CW/90CCW option.
On a mac,you have to select (marquee) the part of the image you want to rotate and then use command T ( the apple key T) to rotate. If you prefer, under Edit find Transform and then Rotate.