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.
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.
The burst mode, also called serial shot mode or continuous shooting mode, allows you to shoot multiple photos in a row.
It allows you to take multiple photos capturing different parts of the scene, and then joins them together into a single photo.