I filmed a video with my digital camera?

but since there was no light.... it's really dark, and you can barely see the people. is there a free software that can lighten it up?

The program that came with your camera is about as free as it gets.

I take it you didn't check the first few minutes to see what the exposure was.

ULead has a trial program you can download, but I haven't really seen a program that will open up the shadow area in a video (30 fps), a five minute film would be over 9000 frames to repair.