Once you are ready to take payment, you must make sure you have already send the order to the kitchen or have hit the tender button depending on your business type.
Once at that state of the transaction you can hit the Ticket button in the menu bar.
Once there all the tender options for your business will appear.
Click the needed button and then follow the instructions give to you on the screen.
If you need detailed information about how to accept a specific form of payment, click here.