If no audio is passing through then you are probably not patched correctly. If you want the stereo main mix to go to the camera do this: Select the master
fader. Cursor up to the routing
button on the
screen (this should be next to where the head amp would be if on an input
channel). Hit enter and it will take you to the patching
page. Select the omni outs that you are using. Note that when you select the master
fader the first time you will be on Left, press it again and you have selected the Right output. Assign the left to the appropriate omni out, press the master
fader's select
button again to go to the right output, then assign it to the next omni out. You can assign an output to as many mixes as you would like, but you cannot assign multiple mixes to one omni out.
This will give you a
line level output of exactly what's going to
FOH. If you want to create a separate mix then you'll need to assign the mixes to the omni outs. This is done in the same way, but you'll have to be on the master
fader layer in order to select the mix masters.
If none of this helped please come back and explain your situation and I'm sure I can step you through it.