How do I make my IPod the default setting on my Mercury Sable Sync system?

I recently purchased a Mercury Sable with Microsoft Sync. To use my IPod with the USB dock I have to go through several steps so I would liked to find out how to make the USB/IPod the default setting on the aux button?How do I make my IPod the default setting on my Mercury Sable Sync system?
I thought Sync was for making phone calls. You do understand that an iPod is NOT a phone, right??? Please explain...