Which cable do I use for iMovie HD?

I looked at the manual for the iMovie and it said I need a firewire cable in order to film a vide with my camera. But I also looked into what a HDMI cable does and it seems like it does the same so which one do I use in order to film a video using my dslr through iMovie?

*I have a NIKON D3100 DSLR*

Added (1). Laura,

So if I get the firewire, is it possible to connect it to the DSLR? Which port do I connect the wire into for the camera? ( A/V Out?) Does this firewire cable allow me to see whatever I film on the iMovie app live? Which one records sound and which one records video? Or is it like.camera is only used for having the quality and my computer itself records the video and sound?

Firewire works the best with iMovie HD.