Popular Tags shows wording used by listings in your keyword results. It can help you find another way to describe your item.
Research one useful phrase
Open your product phrase in Keyword Search.
Look at the products, any filters and the Popular Tags table.
Choose a tag that fits your own item.
Search that phrase to see its searches, engagement and competition.
A tag being common in the sample doesn't tell you how often shoppers search for it.
For a mug, a tag about matching coasters only belongs if your listing offers them. Use your own product details and skip unrelated brands or claims.
Save a phrase you want to use in a Keyword List. A few accurate ideas are more useful than copying another listing's whole tag set.