This feature allows you to assign a lifetime sales of a product/collection to an affiliate so Commission for the selected product will always be assigned to this affiliate no matter if the customer uses affiliate link/coupon or not.
To Connect a product to an affiliate, go to Affiliate & Coupon tab, choose the affiliate you want to connect product and click Connect product, then you just need to search for a product or a collection.
After entering the product/collection, click Connect to assign that product/collection to the chosen affiliate. One product/collection can be assigned to only one affiliate.
In the future, no matter if customer use affiliate link/coupon or not, commissions for the chosen product will still be counted to the assigned affiliate.