How is the cash drawer connected?
The drawer connects either to the drawer socket of a network receipt printer (ip:9100 in the panel) or to a serial port on the counter PC (for example COM1). The open command is sent by the Print Agent on the counter PC.
For which payment types does it open?
By default it opens when a cash payment is recorded, not for card payments or payments sent to the fiscal device. Under General Settings > Hardware and peripherals > "When should the drawer open?" you can instead choose when the payment screen opens, when a payment button is pressed, or when Cash, Card or another payment type is selected.