Help sewing a holiday costume?

I’m making a costume for a masquerade ball this Saturday. It’s a water-sprite costume. I’m making a panel skirt for the bottom which needs to flow gracefully. I don’t have a pattern and no way to get one soon enough. I think I can handle the measurements, shape, etc… But how do I cut the fabric? I know that sometimes you have to cut against the way the fabric is made (ie, “on the bias”) but I haven’t done this in a long time and I’m not quite sure how to do it. Do I need to cut at an angle across the bias? Can anyone describe to me how to cut it? Thank you so much!