This can be used to rotate the image for an interesting effect, or more commonly to correct the image if it is at a slight angle.
If your photo is too bright or dark, you can adjust the brightness in order to get a well-balanced image.
You can take photos within the app. This allows you to do everything from capturing the image to editing all within one app, instead of having to import an image taken with another camera app.
Adjusting the contrast affects the difference between light and dark areas of the image. You can fine tune it to meet your needs, such as increasing the contrast to make your subject stand out more.
Saturation refers to the intensity of colors. It is measured on a scale ranging from 0% (black and white) to 100% (pure colors) at a constant level of brightness. Images with high levels of saturation have vivid colors, while unsaturated images appear greyish.
Adjusting tonal curves allows you to selectively adjust the exposure and contrast within an image.
With manual white balance you can choose the most accurate setting and avoid the green, blue or red hue which can occur in auto mode. You can also change the setting for artistic effect.
On manual SLR cameras, you can do a double exposure resulting in two images being blended into one. You can use the app to replicate this effect by mixing two of your pictures together.
With a self-timer you can set an amount of time to pass before the picture is taken. This allows you to be in the picture yourself and is great for taking photos with friends.