On Big Commerce click on the > Settings link in the top right of the control panel. Choose > Affiliate Settings link from the drop down menu. Then you will have a place to enter the Conversion Tracking Code.

You must copy your conversion tracking code from WOW Trk (if you don't know how to find this ask your account manager), in the code you must add after amount= the following:
%%ORDER_AMOUNT%%

After you have placed the code in the box simply hit Save.