Getting exposure for video isn’t all that much different from getting a good exposure with photography. The only real difference is that neutral density filters are more commonly used with video than they are with stills, so they need to be taken into account more regularly. So, the exposure triangle becomes a square. Well, a trapezoid, really. Shutter speed, aperture, gain (rather than ISO), and neutral density.
In this video, Chris and Jordan from DPReview delve into the topic of video exposure. They discuss the things you need to know to understand the exposure relationship, the difference between T stops and F stops, the 180° shutter rule, and everything else that goes into getting a good exposure for your shot.