User Stories are about the conversations with the user who will be using the product, which ultimately is written on the card. Sometime, it might be difficult to go in the market and find the user to have the conversations. Hence we rely on something called Personas. Personas are the great way to connect with users and the customers and capture their needs. Personas are hypothetical characters that have a name; relevant characteristics such as a role, activities, behaviors, and attitudes; and a goal, which is the problem that has to be addressed or the benefit that should be provided.
Once you have defined the Personas, use their need to define the functionality. functionality can be defined as a part of a User Story and perhaps as an Epic or High-Level Stories.
One thing to keep in mind is, we do not have to provide all the details in a User Story or a High-Level User Story. A great User Story comes from a process of refinement and progressively breaking them into smaller pieces to be able to deliver the value to the customer.