In order to sell a package you must first create the package. To learn how to create a package see: How to Create a Package
You can sell a package from the "Sales" screen or during the normal checkout of an appointment.
If you started the sale from the "Sales" page, or someone is purchasing a package for someone else, make sure to select (or add) the client that will be using the package. You need to assign the package to a client in order to redeem the package later on.
Depending on the settings, click on either "Add Package" or "More" > "Package"
Finish the checkout like you normally would.
The package will be available immediately after the checkout is completed. To view packages go to the "Packages" screen, which may be collapsed under the "More" button in the menu.
If the package was sold through a different platform (for example Groupon) please refer to the following article to learn how to manually add a package for a client: Manage Packages Purchased by Clients