You can click on a customer via the 'Register' module to start a transaction.

If there are no customers with an appointment and all transactions have already been completed, you can start a new transaction with one of the 3 buttons at the top.

In the transaction ticket, you can then click on the "+ Product" button to search for and select a product. If you work with a barcode scanner, you don't have to click on anything. You can immediately scan a product on the opened statement.