Mini DV capture was more reliable with the older iMovie versions. Capturing Mini DV from a camera can be a bit hit or miss with iMovie 10. Mostly it works, and sometimes it doesn't.
You would use firewire cable out of the camera with whatever cables and adapters that you would need to connect to your Mac. The newer Macs do not have a firewire socket, but rather thunderbolt 1, 2, or USB-c. With cables and adapters you can connect to the available socket.
So, 4 pin Firewire to 9 pin Frewire 800 cable, and then whatever adapters and cables are necessary to go from the 9pin Firewire 800 cable to Thunderbolt 1 or 2, and then to USBc (sometimes called Thunderbolt 3)socket if needed.
Take a look at thesurreyfriends post in this thread for more details re the cables and adapters:
https://discussions.apple.com/thread/252658303
-- Rich