Cross-sells: The recommended items you see in your cart.
Upsells: The recommended items you see on a product page.

1. Navigate to the product you want to have cross-sells or upsells.

2. In the left sidebar, you'll see 'Cross-sells' and 'Upsell'.

3. Click on either 'Cross-sells' or 'Upsells', and check off which products you want to display.