So you will need a Mini DisplayPort to USB-c adapter, or cable. Do a web search, or try Amazon, ebay or monoprice for it.It is a brand new iMac, 27", 3.4GHz, 8GB of 2400MHz DDR4 memory with the following connections: Headphone, SDXC card slot, USB 3, Thunderbolt 3 (USB-C), Gigabit Ethernet
The specs to the cinema display I am trying to connect to the iMac can be found here: https://everymac.com/monitors/apple/studio_cinema/specs/apple_cinema_display_23.html