An app must be presentable in a way that users can perceive. For example, someone who is blind cannot see the interface. By making it possible to read the interface, the information can be perceived.
When an image or graph is not described textually, users with a visual impairment cannot perceive the information.
When a video does not have captions, users with a hearing impairment cannot understand the information.
When a button has too low contrast, it might not be clear for users that it can be clicked.
When a form does not have clear labels, it can be unclear to users where and what information is expected from them.