The name of the app is "One Click Upsells" and these "Upsells" can contain any number of Trigger Products and Offers. The Offers themselves can be either cross sells or upsells. It's best you forget about the app name and focus more on the strict use of Upsells and Cross Sells within the app.
Let's consider an example
You want to set up an Upsell (or offer) for your Dining Table product, or in other words, when people add that Dining Table to cart, you would like to create one or more upsells or cross sells.
Trigger - Dining Table
So every time someone adds that Dining Table to cart, they will be presented with 2 cross sells and 1 upsell.
You can have as many cross sells and upsells for an offer/trigger, however we suggest not more than 4 all up. You want to strategically offer cross sells or an upsell that makes sense, and not overwhelm the customer with choice. Offering your most popular Chair with the Table makes sense, so with that in mind, craft offers that make sense and genuinely aim to provide a great and helpful user experience.
You can find out more about upsells and cross sells on our blog post.
For ideas on how to craft really great upsells or cross sells read our article on Proven Cross-selling and Upselling Strategies That Increase Ecommerce Revenue