Here is a UML use case diagram example.
A primary purpose of the model of business use cases and actors is to describe how the business is used by its customers and partners. Activities that directly concern the customer, or partner, as well as supporting or managerial tasks that indirectly concern the external party can be presented. A use case diagram at its simplest is a representation of a user's interaction with the system that shows the relationship between the user and the different use cases in which the user is involved. Major elements of the business use case diagram are shown on the picture here. Note again, both business use case as well as business actor are not defined in UML standard, so you will either need to use some UML tool supporting those or create your own business modeling stereotypes.