Once you have authorised the Cross-sell app to access your Shopify store, a token is stored in the Cross-sell database which will identify your store to the app each time you login. You must be logged in to your store's Shopify admin area in order to use the Cross-sell application (you do not need to be logged in however for the cross-sell products to show in your store).
To get started with installation and customisation, please read the Integrating Cross-Sell into your Shopify theme instructions.
Each Shopify store has configurable resources called metafields that can be accessed and manipulated by authorized applications via the Shopify API (Advanced Programming Interface). Cross-sell is an externally hosted (nothing to do with Shopify) application that allows you to create relationships between products via a user interface and then save the details of those relationships in your store's metafields by using the Shopify API. All of the details of your product relationships are now held within your store which consumes very little storage space. There is no need for your store to "lookup" information on the Cross-sell application site each time a visitor lands on one of your product detail pages or cart/basket page.
Showing Cross-sells in your store
Assuming you have followed the installation instructions and have configured some cross-sells for your store, you should now be seeing your cross-sell selections on your product pages, your cart page or both.
So how does it work?
There are a number of settings available for controlling the display of cross-sells in your store. For a more detailed description of these settings, please refer to our Cross-sell settings documentation. They can be used to control how many products to display, to turn off cross-sell, to override all hand picked cross-sell items with a set of default recommendations plus a few more settings.
Adding Features to Cross-Sell
We plan to develop Cross-sell as it gains momentum and we receive feedback and feature requests.