First of all add some products from the backend of you site as i’ve created.
Now let’s say I want to display product2 as a suggestion whenever a customer have product1 in his cart. To achieve this go to edit screen of product1, now move to the linked product section and search for product2 in the cross-sells field. Add product(s) and hit update.
Now, add the product1 to cart and move to cart page. You’ll see product2 being suggested there.
