Hi there,
1. We upload the csv feed everyday.
The .csv contains important attributes of products, that when you upload to the system, essentially become part of the catalog of products in the system that recommendations will pull from based on the criteria you specify in the activity.
2. There is recommendation -> activities we create the activities add a criteria and select the collection.
3. Add the recommendation metrics.
Here are some definitions that might help your understanding-
"Criteria are rules that determine which products to recommend based on a predetermined set of visitor behaviors. Criteria determine which action will result in which recommendation. You can test multiple recommendation types against each other by adding multiple criteria." (from: Criteria )
And as for collections, "A collection is a set of products or items that are eligible for a recommendation. Commonly, a collection is a set of similar or related items, such as a single product collection." (from: https://marketing.adobe.com/resources/help/en_US/target/recs/index.html?f=c_collections)
All Collections have all the products in the catalog (from the feed).
You could narrow the pool of the recommendations that are generated by a criteria by specifying a particular collection.
Hope this helps!