Google Analytics Conversion and Optimizer Setup Help

I need help setting up conversion tracking for my ebook product. I have Google Analytics already installed on my domain. Here is the sales process: 1. User goes to sales page on [login to view URL] 2. User then goes to the order pages and purchases the product : [login to view URL] 3. Transaction is completed through clickbank 4. User is redirected to the member login page on the subdomain: [login to view URL] 5. Wishlist Member is the membership software that I use for the user to login and download the product. I need someone to help track conversions to the thankyou or registration page in wishlist member which is on a sudomain of the sales page which I will be tracking it from. I am unfamiliar with tracking to a subdomain and the thankyou page can only be viewed after logging in. I am also not sure where to set the conversion tracking with wishlist member. Once conversion is setup I also need to make sure google optimizer is setup so I can split test pages.