Instructions to setup related, up-sells and cross-sell products:
Step 1:- Login to your admin panel.
Step 1:- Go to CATALOG > Products and click on it.

Step 2:- Open the product by click on edit button.

Step 3:- On the product edit page expand the Related Products, Up-Sells, and Cross-Sells tab.

Step 4:- Click on Add Related Products button and select products.

Step 6:- Then click on Add Selected Products button.
Step 7:- Now click on Save button to save your changes.

Step 8:- At last clean your cache and refresh your product page to view your related and upsell products. Cros-sell will be visible on cart page. So, first, you need to add a product to your cart to view cros-sell.

Step 9:- In the same way you can set Up-Sell Products and Cross-Sell Products.
Please contact us at manish@bay20.com or call us at +91-8800519180 for any support related to Magento 2. You can also visit the Magento2 development page to check the services we offer.