If you want to be a good designer (or to understand good design) you need to understand what affordances are and when they are being used properly.
How to determine if something is well designed: The Design Critique Rubric
How do you determine if a feature or product is well designed? You don’t just guess. It’s not a question of personal opinion. Use this rubric to know.
Guidelines for thoughtful product design
You can use the below guidelines to check if your product is ready to ship (or if your prototype is being thoughtful enough), and you can use it as a core way to critique other products.