I've set up a bus and sent four instrument tracks to it.  The signal is going to both the mains and the bus.  How do I make it go to the bus only, so that if the bus fader is turned down all they way, there is no sound from those tracks??
 
Also, how do you get the subject line to BOLD?  I seem to be able to only make the message body bold.

Of course the Bold works now...

NO, the bold didnt work, only in my preview...

Are you using sends on your tracks, with post fader outputs set to the mains?
 
 
If so, set the track outputs to the bus, the bus output to the mains, and delete all the sends from the tracks. This is what most folks would do. Sonar has extensive routing options, (most DAWs do compared to hardware consoles) and there are fifty ways to accomplish things.
 
There are some, though, who like to use sends to a bus which is used for a global reverb effect - similar to how it's done on many live analog mixer consoles.
 
If you're not sure - post what it is you're trying to do and someone will help.

Ok here goes.  I have four VST instrument tracks.  Using the wizard, I created a send, called it "Instruments"  and assigned all four instrument track's outputs to that send.  It is the only bus so far.  My assumption was that if I did this I could control the output level of all four tracks at the same time using the fader on the send.  However, I can turn the fader on the send all the way down, and the instruments can still be heard in the mains.  Raising the send fader does add more volume, so I know the signal is going there.  
 
How do I route the instrument track's signals so that they go the bus only, and not the mains?

Get rid of the send. Assign the actual track output to the buss. 
If your in console view the in/out should be below the fader. Highlight all the audio channels that you want to send to that bus . Hold  Ctrl and change the output assignment to the buss that you want. 

Ah I see, so the send is what is causing the signal to go to both. Thanks so much.

Marc,
Next time just create a buss yourself, and assign things to it (either outputs or sends) - rather than using the wizard. It gives you a better idea of what you're actually doing ;-)