Click the 
icon on the toolbar.
This will open the Output Configuration
dialog box.
Make sure that your main soundcard is selected in the "ON-AIR" output device and that Enabled option is selected.
Select the Right channel option in the Use on-air device for cue: options.
Close the Output configuration dialog box.
To test, play your favorite Ots files.
Select the Mixer
by clicking twice on the 
button on the toolbar.
Click the Cue button. You will notice the on-air output through the left channel and the cue channel is output through the right channel.
Tip: You may notice the ON-AIR signal through the cue channel. For instructions on how to remove the "ON-AIR" signal from the cue channel click here.
How to remove "ON-AIR" signal from the cue channel
How to set up your soundcard (main channel)