On Facebook, many people post videos up from their day, trips, or celebrations. I don't think they bring their computers with them on all those trips and tape what is going on with a camera on their computers or on their cellphones. Can I use a video from my video camera and put it on Facebook? How do you do it?

umm... you take a video on ur camera...
upload it on your computer.
upload it on facebook videos... ahaha .

WALAAAAAAAAAAAA!

Where do you plug it in? Will it need a system to download to?

You get a USB cord that's compatible to your camera. You need to figure out what model you have to do that.
It will just upload to your computer when you plug it in (most likely a folder like "Pictures" or "Videos"). You then go to the Facebook video uploader and follow the steps to upload your video onto Facebook.

Thanks for your help.

no problem.