This blog explains few of the capabilities of Launch function in PowerApps.
I would like to directly jump into an example as it is quite simple and self-explanatory. Here is a PowerApp which is connected to Dynamics 365 for Finance and Operations customers entity through the connector. The App is reading customer data and showing some important information on Customer Details page. For an end user (maybe a salesperson), along with the required or some important customer details, you can also provide him/her with easy ways to connect with the customer right from within the App. Give ability to users on a PowerApp to Visit customer’s website, Call primary phone number, Email Primary contact or Get directions on the map to go meet them directly, all using one function – Launch!