The mixer is designed to work intuitively like a hardware mixing console. The faders control volume. The knobs at the top control the inline FX (see the session edit screen) and any send FX are added below with colour coding matching the send channel. Playing channels have colour coded faders matching their channel colour.
The faders are a little more varied on the video side. For a channel that is generating video, they control the brightness of the video output. For master FX they mostly control the mix of that effect, but for some such as Contrast they control another parameter - in that case the contrast parameter. Knobs are added for each playing clip and can be set to respond to audio from the adjacent audio channel. Set in the centre they do not respond to the audio, they can respond positively or negatively depending on their position relative to the centre.