Crop and straighten is simple and streamlined. Just zoom and drag to change the crop area, then tap Save to store your cropped photo in the Camera Roll. Theres no need to fiddle with small resize handlers; the cropped area is always displayed full-screen so you see exactly what youll get.

Pinch in and out with two fingers to change the crop area, then drag to move it. Choose from regular aspect ratios as 1:2, 2:3 and 3:4, or classic medium and large format film sizes as 4:5, 6:7 and 1:1 (square).

Rotate with two fingers to unlock straighten mode. A grid will appear to help you align. The rotation snaps at 90 angles so you can easily fix a photo where the camera got the orientation wrong.

Crop and straighten can now also retain date and time, location and other camera information (Exif headers) in the cropped image.

Use Crop and Straighten:

to improve the composition of your photos,
to straighten crooked images (skewed horizon, slanted building or lamp post, etc.),
as a digital zoom for your iPhone camera,
to remove unwanted elements from your photo,
to fix a photo where the orientation is wrong, or
simply to choose a different aspect ratio.
Source:DSLRPhoto