This article applies to the old designer. Not sure which designer you have? Check here.
Step 1 - Get the Conversion Pixel
If you need help setting up Google Adwords Conversion Pixels use their guide.
Step 2 - Find the Right Spot
You can track conversions through a wide variety of actions that a customer may take on your website. The most common place to track conversions is on the "Thank You" page after a customer has completed the checkout. Tracking conversions here will let you know how many orders have been completed that originated from your Google Adwords Ad.
Note: This process will vary slightly depending on how customized your theme has become. The important thing is to make sure and include the facebook code inside of your main content block in the template. This block is typically named "{% block page_content %}".