Data storage can be done in so many ways that a 'type' is assigned to them. There are text, image and video types. Data types can be stored on the device or saved to an external storage, i.e. sd card or usb drive.
There are a lot of different restrictions and permissions required for an app to access local storage. There are also several different programming considerations. For instance available storage space can be limited. Learn more about data storage and mobile apps. Here is the long answer.