Simple:
* The books were organized by category.
* This product falls into the category of home appliances.
* The store has a wide category of items to choose from.
More complex:
* The study found that people in the category of "high income earners" were more likely to invest in the stock market.
* The new website allows users to filter products by category and price.
* This movie fits into the category of action thrillers.
* His argument fell into the category of "misleading" rather than "factual."
Figurative:
* I'd put his behavior in the category of "completely unacceptable."
* Her painting style doesn't fit into any traditional category.
The key is to think of "category" as a way to group or classify things. You can use it to talk about:
* Physical things: books, products, items in a store
* Concepts: types of behavior, ideas, genres of entertainment
* People: groups based on income, age, interests